Manipulating the bioenergetics of alloreactive T cells causes their selective apoptosis and arrests graft-versus-host disease

Deciphering metabolic crosstalk in context: lessons from inflammatory diseases

Metabolism plays a crucial role in regulating the function of immune cells in both health and disease, with altered metabolism contributing to the pathogenesis of cancer and many inflammatory diseases. The local microenvironment has a profound impact on the metabolism of immune cells. Therefore, immunological and metabolic heterogeneity as well as the spatial organization of cells in tissues should be taken into account when studying immunometabolism. Here, we highlight challenges of investigating metabolic communication. Additionally, we review the capabilities and limitations of current technologies for studying metabolism in inflamed microenvironments, including single-cell omics techniques, flow cytometry-based methods (Met-Flow, single-cell energetic metabolism by profiling translation inhibition (SCENITH)), cytometry by time of flight (CyTOF), cellular indexing of transcriptomes and epitopes by sequencing (CITE-Seq), and mass spectrometry imaging. Considering the importance of metabolism in regulating immune cells in diseased states, we also discuss the applications of metabolomics in clinical research, as well as some hurdles to overcome to implement these techniques in standard clinical practice. Finally, we provide a flowchart to assist scientists in designing effective strategies to unravel immunometabolism in disease-relevant contexts.

Association between intracellular adenosine triphosphate content of CD4+ T lymphocytes and mortality in sepsis patients: A prospective observational study

OBJECTIVE

This study aimed to link intracellular adenosine triphosphate content in CD4+ T lymphocytes (CD4+ iATP) with sepsis patient mortality, seeking a new predictive biomarker for outcomes and enhanced management.

METHODS

61 sepsis patients admitted to the Intensive Care Unit between October 2021 and November 2022 were enrolled. iATP levels were gauged using whole blood CD4+ T cells stimulated with mitogen PHA-L. Based on CD4+ iATP levels (<132.24 and ≥132.24 ng/mL), patients were categorized into two groups. The primary endpoint was all-cause mortality. To identify factors associated with mortality, both univariate and multivariate Cox proportional hazard analyses were conducted.

RESULTS

Of the patients, 40 had high CD4+ iATP levels (≥132.24 ng/mL) and 21 had low levels (<132.24 ng/mL). In a 28-day follow-up, 21 (34.4%) patients perished. Adjusting for confounders like SOFA score, APACHE II score, lactic acid, and albumin, those with low CD4+ iATP had three- to fivefold higher mortality risk compared to high CD4+ iATP patients (61.9% vs. 20.0%; hazard ratio [95% confidence interval], Model 1: 4.515 [1.276-15.974], p = .019, Model 2: 3.512 [1.197-10.306], p = .022). CD4+ iATP correlated positively with white blood cell and neutrophil counts but not with lymphocytes, CD3, and CD4 counts.

CONCLUSIONS

Low CD4+ iATP levels were associated with a higher risk of mortality in sepsis patients. Measurement of CD4+ iATP may serve as a useful tool for identifying patients at a higher risk of mortality and could potentially provide a basis for clinical treatment. Further research is warranted to fully elucidate the underlying mechanisms of this association.

Metabolic instruction of the graft-versus-leukemia immunity

Allogeneic hematopoietic cell transplantation (allo-HCT) is frequently performed to cure hematological malignancies, such as acute myeloid leukemia (AML), through the graft-versus-leukemia (GVL) effect. In this immunological process, donor immune cells eliminate residual cancer cells in the patient and exert tumor control through immunosurveillance. However, GVL failure and subsequent leukemia relapse are frequent and associated with a dismal prognosis. A better understanding of the mechanisms underlying AML immune evasion is essential for developing novel therapeutic strategies to boost the GVL effect. Cellular metabolism has emerged as an essential regulator of survival and cell fate for both cancer and immune cells. Leukemia and T cells utilize specific metabolic programs, including the orchestrated use of glucose, amino acids, and fatty acids, to support their growth and function. Besides regulating cell-intrinsic processes, metabolism shapes the extracellular environment and plays an important role in cell-cell communication. This review focuses on recent advances in the understanding of how metabolism might affect the anti-leukemia immune response. First, we provide a general overview of the mechanisms of immune escape after allo-HCT and an introduction to leukemia and T cell metabolism. Further, we discuss how leukemia and myeloid cell metabolism contribute to an altered microenvironment that impairs T cell function. Next, we review the literature linking metabolic processes in AML cells with their inhibitory checkpoint ligand expression. Finally, we focus on recent findings concerning the role of systemic metabolism in sustained GVL efficacy. While the majority of evidence in the field still stems from basic and preclinical studies, we discuss translational findings and propose further avenues for bridging the gap between bench and bedside.

Mitochondrial-targeted curcumin inhibits T-cell activation via Nrf2 and inhibits graft-versus-host-disease in a mouse model

Anti-inflammatory and immune suppressive agents are required to moderate hyper-activation of lymphocytes under disease conditions or organ transplantation. However, selective disruption of mitochondrial redox has not been evaluated as a therapeutic strategy for suppression of T-cell-mediated pathologies. Using mitochondrial targeted curcumin (MitoC), we studied the effect of mitochondrial redox modulation on T-cell responses by flow cytometry, transmission electron microscopy, transcriptomics, and proteomics, and the role of Nrf2 was studied using Nrf2- /- mice. MitoC decreased mitochondrial TrxR activity, enhanced mitochondrial ROS (mROS) production, depleted mitochondrial glutathione, and suppressed activation-induced increase in mitochondrial biomass. This led to suppression of T-cell responses and metabolic reprogramming towards Treg differentiation. MitoC induced nuclear translocation and DNA binding of Nrf2, leading to upregulation of Nrf2-dependent genes and proteins. MitoC-mediated changes in mitochondrial redox and modulation of T-cell responses are abolished in Nrf2- /- mice. Restoration of mitochondrial thiols abrogated inhibition of T-cell responses. MitoC suppressed alloantigen-induced lymphoblast formation, inflammatory cytokines, morbidity, and mortality in acute graft-versus-host disease mice. Disruption of mitochondrial thiols but not mROS increase inculcates an Nrf2-dependent immune-suppressive disposition in T cells for the propitious treatment of graft-versus-host disease.

Fatty Acids Play a Critical Role in Mitochondrial Oxidative Phosphorylation in Effector T Cells in Graft-versus-Host Disease

Although the role of aerobic glycolysis in activated T cells has been well characterized, whether and how fatty acids (FAs) contribute to donor T cell function in allogeneic hematopoietic stem cell transplantation is unclear. Using xenogeneic graft-versus-host disease (GVHD) models, this study demonstrated that exogenous FAs serve as a crucial source of mitochondrial respiration in donor T cells in humans. By comparing human T cells isolated from wild-type NOD/Shi-scid-IL2rγnull (NOG) mice with those from MHC class I/II-deficient NOG mice, we found that donor T cells increased extracellular FA uptake, the extent of which correlates with their proliferation, and continued to increase FA uptake during effector differentiation. Gene expression analysis showed the upregulation of a wide range of lipid metabolism-related genes, including lipid hydrolysis, mitochondrial FA transport, and FA oxidation. Extracellular flux analysis demonstrated that mitochondrial FA transport was required to fully achieve the mitochondrial maximal respiration rate and spare respiratory capacity, whereas the substantial disruption of glucose supply by either glucose deprivation or mitochondrial pyruvate transport blockade did not impair oxidative phosphorylation. Taken together, FA-driven mitochondrial respiration is a hallmark that differentiates TCR-dependent T cell activation from TCR-independent immune response after hematopoietic stem cell transplant.

Inflammasome activation occurs in CD4+ and CD8+ T cells during graft-versus-host disease

A severe complication of hematopoietic stem cell transplantation is graft-versus-host disease (GvHD), a reaction that occurs following the transfer of donor immune cells (the graft) into an allogeneic host. Transplanted cells recognize host alloantigens as foreign, resulting in the activation of donor T cells and migration of these pathological cells into host tissues. In this study, we found that caspase-1 is activated in alloreactive murine and human CD4+ and CD8+ T cells early during acute GvHD (aGvHD). The presence of inflammasome-bound active caspase-1 (p33) and ASC-speck formation confirmed inflammasome activation in these cells. We further measured gasdermin D (GSDMD) cleavage and IL-18 secretion from alloreactive T cells ex vivo. Isolated T cells with high levels of active caspase-1 had a strong inflammatory transcriptional signature and a metabolic phenotype similar to inflammatory myeloid cells, including the upregulation of proinflammatory cytokines and metabolic switch from oxidative phosphorylation to aerobic glycolysis. We also observed oxidative stress, mitochondrial dysfunction, and cell death phenotypes consistent with inflammatory cell death in alloreactive T cells. For the first time, this study characterizes caspase-1 activation in transplanted T cells during aGvHD, using mouse and human models, adding to a body of literature supporting inflammasome function in cells of the adaptive immune system.

Donor T cell STAT3 deficiency enables tissue PD-L1-dependent prevention of graft-versus-host disease while preserving graft-versus-leukemia activity

STAT3 deficiency (STAT3-/-) in donor T cells prevents graft-versus-host disease (GVHD), but the impact on graft-versus-leukemia (GVL) activity and mechanisms of GVHD prevention remains unclear. Here, using murine models of GVHD, we show that STAT3-/- donor T cells induced only mild reversible acute GVHD while preserving GVL effects against nonsusceptible acute lymphoblastic leukemia (ALL) cells in a donor T cell dose-dependent manner. GVHD prevention depended on programmed death ligand 1/programmed cell death protein 1 (PD-L1/PD-1) signaling. In GVHD target tissues, STAT3 deficiency amplified PD-L1/PD-1 inhibition of glutathione (GSH)/Myc pathways that regulate metabolic reprogramming in activated T cells, with decreased glycolytic and mitochondrial ATP production and increased mitochondrial ROS production and dysfunction, leading to tissue-specific deletion of host-reactive T cells and prevention of GVHD. Mitochondrial STAT3 deficiency alone did not reduce GSH expression or prevent GVHD. In lymphoid tissues, the lack of host-tissue PD-L1 interaction with PD-1 reduced the inhibition of the GSH/Myc pathway despite reduced GSH production caused by STAT3 deficiency and allowed donor T cell functions that mediate GVL activity. Therefore, STAT3 deficiency in donor T cells augments PD-1 signaling-mediated inhibition of GSH/Myc pathways and augments dysfunction of T cells in GVHD target tissues while sparing T cells in lymphoid tissues, leading to prevention of GVHD while preserving GVL effects.

Interplay between metabolic reprogramming and post-translational modifications: from glycolysis to lactylation

Cellular metabolism plays a critical role in determining the fate and function of cells. Metabolic reprogramming and its byproducts have a complex impact on cellular activities. In quiescent T cells, oxidative phosphorylation (OXPHOS) is the primary pathway for survival. However, upon antigen activation, T cells undergo rapid metabolic reprogramming, characterized by an elevation in both glycolysis and OXPHOS. While both pathways are induced, the balance predominantly shifts towards glycolysis, enabling T cells to rapidly proliferate and enhance their functionality, representing the most distinctive signature during activation. Metabolic processes generate various small molecules resulting from enzyme-catalyzed reactions, which also modulate protein function and exert regulatory control. Notably, recent studies have revealed the direct modification of histones, known as lactylation, by lactate derived from glycolysis. This lactylation process influences gene transcription and adds a novel variable to the regulation of gene expression. Protein lactylation has been identified as an essential mechanism by which lactate exerts its diverse functions, contributing to crucial biological processes such as uterine remodeling, tumor proliferation, neural system regulation, and metabolic regulation. This review focuses on the metabolic reprogramming of T cells, explores the interplay between lactate and the immune system, highlights the impact of lactylation on cellular function, and elucidates the intersection of metabolic reprogramming and epigenetics.

AMPK Drives Both Glycolytic and Oxidative Metabolism in T Cells During Graft-versus-host Disease

Allogeneic T cells reprogram their metabolism during acute graft-versus-host disease (GVHD) in a process reliant on the cellular energy sensor AMP-activated protein kinase (AMPK). Deletion of AMPK in donor T cells limits GVHD but still preserves homeostatic reconstitution and graft-versus-leukemia (GVL) effects. In the current studies, murine T cells lacking AMPK decreased oxidative metabolism at early timepoints post-transplant and were also unable to mediate a compensatory increase in glycolysis following inhibition of the electron transport chain. Human T cells lacking AMPK gave similar results, with glycolytic compensation impaired both in vitro and following expansion in vivo in a modified model of GVHD. Immunoprecipitation of proteins from day 7 allogeneic T cells, using an antibody specific to phosphorylated AMPK targets, recovered lower levels of multiple glycolysis-related proteins including the glycolytic enzymes aldolase, enolase, pyruvate kinase M (PKM), and glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Functionally, murine T cells lacking AMPK exhibited impaired aldolase activity following anti-CD3/CD28 stimulation and a decrease in GAPDH activity on day 7 post-transplant. Importantly, these changes in glycolysis correlated with an impaired ability of AMPK KO T cells to produce significant amounts of interferon gamma (IFNγ) upon antigenic re-stimulation. Together these data highlight a significant role for AMPK in controlling oxidative and glycolytic metabolism in both murine and human T cells during GVHD and endorse further study of AMPK inhibition as a potential target for future clinical therapies.

KEY POINTS

AMPK plays a key role in driving both and oxidative and glycolytic metabolism in T cells during graft-versus-host disease (GVHD)Absence of AMPK simultaneously impairs both glycolytic enzyme activity, most notably by aldolase, and interferon gamma (IFNγ) production.

GC-MS based untargeted metabolomics reveals the metabolic response of earthworm (Eudrilus eugeniae) after chronic combinatorial exposure to three different pesticides

In this study GC-MS-based untargeted metabolomics was used to identify the metabolic response of earthworm; Eudrilus eugeniae exposed to sub-lethal concentrations of chlorpyrifos-CHL, cypermethrin-CYP, Glyphosate-GLY, and Combined-C (all three pesticides) at the concentrations of 3, 6, and 12 mg/kg. Principal component analysis of the obtained datasets revealed a clear distinction between the control and treatment groups. The mean weight of the worms in the treated groups decreased significantly (p < 0.05). Among the identified metabolites, oleic acid (~ 93.47%), lysine (~ 92.20%), glutamic acid (~ 91.81%), leucine (~ 90.20%), asparagine (~ 94.20%), methionine (~ 92.27%), malic acid (~ 93.37%), turanose (~ 95.04%), maltose (~ 92.36%), cholesta-3,5-diene (~ 86.11%), galactose (~ 93.20%), cholesterol (~ 91.56%), tocopherol (~ 85.09%), decreased significantly (p < 0.05), whereas myoinositol (~ 83%) and isoleucine (78.09%) increased significantly (p < 0.05) upon exposure to the CHL, CYP, GLY, and C. Overall, the findings suggest that earthworms might be a new entry point for the pesticides into the food chain. The present study highlights that metabolomics can be a reliable approach to understand the effect of different xenobiotics including pesticides on the metabolic response of earthworms.

Glucocorticoid and glycolysis inhibitors cooperatively abrogate acute graft-versus-host disease

Although glucorticosteroids (GCs) are the standard first-line therapy for acute graft-versus-host disease (aGvHD), nearly 50% of aGvHD patients have no response to GCs. The role of T cell metabolism in murine aGvHD was recently reported. However, whether GCs and metabolism regulators could cooperatively suppress T cell alloreactivity and ameliorate aGvHD remains to be elucidated. Increased glycolysis, characterized by elevated 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), and higher rates of glucose consumption and lactate production were found in T cells from aGvHD patients. Genetic upregulation of PFKFB3 induced T cell proliferation and differentiation into proinflammatory cells. In a humanized mouse model, PFKFB3-overexpressing or PFKFB3-silenced T cells aggravated or prevented aGvHD, respectively. Importantly, our integrated data from patient samples in vitro, in a humanized xenogeneic murine model of aGvHD and graft-versus-leukaemia (GVL) demonstrate that GCs combined with a glycolysis inhibitor could cooperatively reduce the alloreactivity of T cells and ameliorate aGvHD without loss of GVL effects. Together, the current study indicated that glycolysis is critical for T cell activation and induction of human aGvHD. Therefore, the regulation of glycolysis offers a potential pathogenesis-oriented therapeutic strategy for aGvHD patients. GCs combined with glycolysis inhibitors promises to be a novel first-line combination therapy for aGvHD patients.

Metabolic reprogramming by miRNAs in the tumor microenvironment: Focused on immunometabolism

MicroRNAs (miRNAs) are emerging as a significant modulator of immunity, and their abnormal expression/activity has been linked to numerous human disorders, such as cancer. It is now known that miRNAs potentially modulate the production of several metabolic processes in tumor-associated immune cells and indirectly via different metabolic enzymes that affect tumor-associated signaling cascades. For instance, Let-7 has been identified as a crucial modulator for the long-lasting survival of CD8+ T cells (naive phenotypes) in cancer by altering their metabolism. Furthermore, in T cells, it has been found that enhancer of zeste homolog 2 (EZH2) expression is controlled via glycolytic metabolism through miRNAs in patients with ovarian cancer. On the other hand, immunometabolism has shown us that cellular metabolic reactions and processes not only generate ATP and biosynthetic intermediates but also modulate the immune system and inflammatory processes. Based on recent studies, new and encouraging approaches to cancer involving the modification of miRNAs in immune cell metabolism are currently being investigated, providing insight into promising targets for therapeutic strategies based on the pivotal role of immunometabolism in cancer. Throughout this overview, we explore and describe the significance of miRNAs in cancer and immune cell metabolism.

The role of AMP-activated protein kinase in GVHD-causing T cells

Allogeneic stem cell transplantation is a curative therapy for multiple hematologic disorders. However, this life-saving procedure is often complicated by acute graft-versus-host disease (GVHD), where donor T cells attack tissues in the recipient's skin, liver, and gastrointestinal tract. Previous research has demonstrated that GVHD-causing T cells undergo significant metabolic reprogramming during disease pathogenesis, with an increased reliance on oxidative metabolism. This dependence makes metabolic modulation a potential approach to treat and/or prevent GVHD. Here, we provide an overview on the metabolic changes adopted by allogeneic T cells during disease initiation, highlighting the role played by AMP-activated protein kinase (AMPK) and identifying ways in which these insights might be leveraged to therapeutic advantage clinically.

Metabolic Reprogramming of Alloreactive T Cells Through TCR/MYC/mTORC1/E2F6 Signaling in aGvHD Patients

Acute graft-versus-host disease (aGvHD) is the most common complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and significantly linked with morbidity and mortality. Although much work has been engaged to investigate aGvHD pathogenesis, the understanding of alloreactive T-cell activation remains incomplete. To address this, we studied transcriptional activation of carbohydrate, nucleotide, tricarboxylic acid (TCA) cycle, and amino acid metabolism of T cells before aGvHD onset by mining the Gene Expression Omnibus (GEO) datasets. Glycolysis had the most extensive correlation with other activated metabolic sub-pathways. Through Pearson correlation analyses, we found that glycolytic activation was positively correlated with activated CD4 memory T-cell subset and T-cell proliferation and migration. T-cell receptor (TCR), mechanistic target of rapamycin complex 1 (mTORC1), myelocytomatosis oncogene (MYC) signaling pathways and E2F6 might be “master regulators” of glycolytic activity. aGvHD predictive model constructed by glycolytic genes (PFKP, ENO3, and GAPDH) through logistic regression showed high predictive and discriminative value. Furthermore, higher expressions of PFKP, ENO3, and GAPDH in alloreactive T cells were confirmed in our pre-aGvHD patient cohort. And the predictive value of the aGvHD risk model was also validated. In summary, our study demonstrated that glycolytic activation might play a pivotal function in alloreactive T-cell activation before aGvHD onset and would be the potential target for aGvHD therapy.

T-cell Exhaustion in Organ Transplantation

Exhaustion of T cells occurs in response to long-term exposure to self and foreign antigens. It limits T cell capacity to proliferate and produce cytokines, leading to an impaired ability to clear chronic infections or eradicate tumors. T-cell exhaustion is associated with a specific transcriptional, epigenetic, and metabolic program and characteristic cell surface markers' expression. Recent studies have begun to elucidate the role of T-cell exhaustion in transplant. Higher levels of exhausted T cells have been associated with better graft function in kidney transplant recipients. In contrast, reinvigorating exhausted T cells by immune checkpoint blockade therapies, while promoting tumor clearance, increases the risk of acute rejection. Lymphocyte depletion and high alloantigen load have been identified as major drivers of T-cell exhaustion. This could account, at least in part, for the reduced rates of acute rejection in organ transplant recipients induced with thymoglobulin and for the pro-tolerogenic effects of a large organ such as the liver. Among the drugs that are widely used for maintenance immunosuppression, calcineurin inhibitors have a contrasting inhibitory effect on exhaustion of T cells, while the influence of mTOR inhibitors is still unclear. Harnessing or encouraging the natural processes of exhaustion may provide a novel strategy to promote graft survival and transplantation tolerance.

Targeting Glycolysis in Alloreactive T Cells to Prevent Acute Graft-Versus-Host Disease While Preserving Graft-Versus-Leukemia Effect

Alloreactive donor T cells undergo extensive metabolic reprogramming to become activated and induce graft-versus-host disease (GVHD) upon alloantigen encounter. It is generally thought that glycolysis, which promotes T cell growth and clonal expansion, is employed in this process. However, conflicting data have been reported regarding the requirement of glycolysis to induce T cell-mediated GVHD due to the lack of T cell-specific treatments using glycolysis inhibitors. Importantly, previous studies have not evaluated whether graft-versus-leukemia (GVL) activity is preserved in donor T cells deficient for glycolysis. As a critical component affecting the clinical outcome, it is necessary to assess the anti-tumor activity following treatment with metabolic modulators in preclinical models. In the present study, we utilized T cells selectively deficient for glucose transporter 1 (Glut1^T-KO), to examine the role of glycolysis exclusively in alloreactive T cells without off-targeting effects from antigen presenting cells and other cell types that are dependent on glycolysis. We demonstrated that transfer of Glut1^T-KO T cells significantly improved acute GVHD outcomes through increased apoptotic rates, impaired expansion, and decreased proinflammatory cytokine production. In addition to impaired GVHD development, donor Glut1^T-KO T cells mediated sufficient GVL activity to protect recipients from tumor development. A clinically relevant approach using donor T cells treated with a small molecule inhibitor of glycolysis, 2-Deoxy-D-glucose ex vivo, further demonstrated protection from tumor development. These findings indicate that treatment with glycolysis inhibitors prior to transplantation selectively eliminates alloreactive T cells, but spares non-alloreactive T cells including those that protect against tumor growth. The present study has established a definitive role for glycolysis in acute GVHD and demonstrated that acute GVHD can be selectively prevented through targeting glycolysis.

T-Cell Metabolism in Graft Versus Host Disease

Allogeneic-hematopoietic stem cell transplantation (allo-HSCT) represents the only curative treatment option for numerous hematological malignancies. Elimination of malignant cells depends on the T-cells' Graft-versus-Tumor (GvT) effect. However, Graft-versus-Host-Disease (GvHD), often co-occurring with GvT, remains an obstacle for therapeutic efficacy. Hence, approaches, which selectively alleviate GvHD without compromising GvT activity, are needed. As already explored for autoimmune and inflammatory disorders, immuno-metabolic interventions pose a promising option to address this unmet challenge. Being embedded in a complex regulatory framework, immunological and metabolic pathways are closely intertwined, which is demonstrated by metabolic reprograming of T-cells upon activation or differentiation. In this review, current knowledge on the immuno-metabolic signature of GvHD-driving T-cells is summarized and approaches to metabolically interfere are outlined. Furthermore, we address the metabolic impact of standard medications for GvHD treatment and prophylaxis, which, in conjunction with the immuno-metabolic profile of alloreactive T-cells, could allow more targeted interventions in the future.

Immunometabolic Therapeutic Targets of Graft-versus-Host Disease (GvHD)

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative option in the treatment of aggressive malignant and non-malignant blood disorders. However, the benefits of allo-HSCT can be compromised by graft-versus-host disease (GvHD), a prevalent and morbid complication of allo-HSCT. GvHD occurs when donor immune cells mount an alloreactive response against host antigens due to histocompatibility differences between the donor and host, which may result in extensive tissue injury. The reprogramming of cellular metabolism is a feature of GvHD that is associated with the differentiation of donor CD4+ cells into the pathogenic Th1 and Th17 subsets along with the dysfunction of the immune-suppressive protective T regulatory cells (Tregs). The activation of glycolysis and glutaminolysis with concomitant changes in fatty acid oxidation metabolism fuel the anabolic activities of the proliferative alloreactive microenvironment characteristic of GvHD. Thus, metabolic therapies such as glycolytic enzyme inhibitors and fatty acid metabolism modulators are a promising therapeutic strategy for GvHD. We comprehensively review the role of cellular metabolism in GvHD pathogenesis, identify candidate therapeutic targets, and describe potential strategies for augmenting immunometabolism to ameliorate GvHD.

Recent Metabolic Advances for Preventing and Treating Acute and Chronic Graft Versus Host Disease

The therapeutic efficacy of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is limited by the development of graft-versus-host disease (GVHD). In GVHD, rigorous pre-conditioning regimen resets the immune landscape and inflammatory milieu causing immune dysregulation, characterized by an expansion of alloreactive cells and a reduction in immune regulatory cells. In acute GVHD (aGVHD), the release of damage- and pathogen- associated molecular patterns from damaged tissue caused by the conditioning regimen sets the stage for T cell priming, activation and expansion further exacerbating tissue injury and organ damage, particularly in the gastrointestinal tract. Studies have shown that donor T cells utilize multiple energetic and biosynthetic pathways to mediate GVHD that can be distinct from the pathways used by regulatory T cells for their suppressive function. In chronic GVHD (cGVHD), donor T cells may differentiate into IL-21 producing T follicular helper cells or tissue resident T helper cells that cooperate with germinal center B cells or memory B cells, respectively, to produce allo- and auto-reactive antibodies with subsequent tissue fibrosis. Alternatively, donor T cells can become IFN- γ/IL-17 cytokine expressing T cells that mediate sclerodermatous skin injury. Patients refractory to the first line standard regimens for GVHD treatment have a poor prognosis indicating an urgent need for new therapies to restore the balance between effector and regulatory immune cells while preserving the beneficial graft-versus-tumor effect. Emerging data points toward a role for metabolism in regulating these allo- and auto-immune responses. Here, we will discuss the preclinical and clinical data available on the distinct metabolic demands of acute and chronic GVHD and recent efforts in identifying therapeutic targets using metabolomics. Another dimension of this review will examine the changing microbiome after allo-HSCT and the role of microbial metabolites such as short chain fatty acids and long chain fatty acids on regulating immune responses. Lastly, we will examine the metabolic implications of coinhibitory pathway blockade and cellular therapies in allo-HSCT. In conclusion, greater understanding of metabolic pathways involved in immune cell dysregulation during allo-HSCT may pave the way to provide novel therapies to prevent and treat GVHD.

Regulatory T Cell Therapy of Graft-versus-Host Disease: Advances and Challenges

Graft-versus-host disease (GVHD) is the leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Immunomodulation using regulatory T cells (Tregs) offers an exciting option to prevent and/or treat GVHD as these cells naturally function to maintain immune homeostasis, can induce tolerance following HSCT, and have a tissue reparative function. Studies to date have established a clinical safety profile for polyclonal Tregs. Functional enhancement through genetic engineering offers the possibility of improved potency, specificity, and persistence. In this review, we provide the most up to date preclinical and clinical data on Treg cell therapy with a particular focus on GVHD. We discuss the different Treg subtypes and highlight the pharmacological and genetic approaches under investigation to enhance the application of Tregs in allo-HSCT. Lastly, we discuss the remaining challenges for optimal clinical translation and provide insights as to future directions of the field.

Fueling the Revolution: Targeting Metabolism to Enhance Immunotherapy

The success of immune-checkpoint blockade and chimeric antigen receptor (CAR) T cell therapies has established the remarkable capacity of the immune system to fight cancer. Over the past several years, it has become clear that immune cell responses to cancer are critically dependent upon metabolic programs that are specific to both immune cell type and function. Metabolic features of cancer cells and the tumor microenvironment impose constraints on immune cell metabolism that can favor immunosuppressive phenotypes and block antitumor responses. Advances in both preclinical and clinical studies have demonstrated that metabolic interventions can dramatically enhance the efficacy of immune-based therapies for cancer. As such, understanding the metabolic requirements of immune cells in the tumor microenvironment, as well as the limitations imposed therein, can have significant benefits for informing both current practice and future research in cancer immunotherapy.

Deletion of AMPK minimizes graft-versus-host disease through an early impact on effector donor T cells

Allogeneic hematopoietic stem cell transplantation is a viable treatment for multiple hematologic diseases, but its application is often limited by graft-versus-host disease (GVHD), where donor T cells attack host tissues in the skin, liver, and gastrointestinal tract. Here, we examined the role of the cellular energy sensor AMP kinase (AMPK) in alloreactive T cells during GVHD development. Early posttransplant, AMPK activity increased more than 15-fold in allogeneic T cells, and transplantation of T cells deficient in both AMPKα1 and AMPKα2 decreased GVHD severity in multiple disease models. Importantly, a lack of AMPK lessened GVHD without compromising antileukemia responses or impairing lymphopenia-driven immune reconstitution. Mechanistically, absence of AMPK decreased both CD4⁺ and CD8⁺ effector T cell numbers as early as day 3 posttransplant, while simultaneously increasing regulatory T cell (Treg) percentages. Improvements in GVHD resulted from cell-intrinsic perturbations in conventional effector T cells as depletion of donor Tregs had minimal impact on AMPK-related improvements. Together, these results highlight a specific role for AMPK in allogeneic effector T cells early posttransplant and suggest that AMPK inhibition may be an innovative approach to mitigate GVHD while preserving graft-versus-leukemia responses and maintaining robust immune reconstitution.

Spatiotemporal single-cell profiling reveals that invasive and tissue-resident memory donor CD8+ T cells drive gastrointestinal acute graft-versus-host disease

Organ infiltration by donor T cells is critical to the development of acute graft-versus-host disease (aGVHD) in recipients after allogeneic hematopoietic stem cell transplant (allo-HCT). However, deconvoluting the transcriptional programs of newly recruited donor T cells from those of tissue-resident T cells in aGVHD target organs remains a challenge. Here, we combined the serial intravascular staining technique with single-cell RNA sequencing to dissect the tightly connected processes by which donor T cells initially infiltrate tissues and then establish a pathogenic tissue residency program in a rhesus macaque allo-HCT model that develops aGVHD. Our results enabled creation of a spatiotemporal map of the transcriptional programs controlling donor CD8⁺ T cell infiltration into the primary aGVHD target organ, the gastrointestinal (GI) tract. We identified the large and small intestines as the only two sites demonstrating allo-specific, rather than lymphodepletion-driven, T cell infiltration. GI-infiltrating donor CD8⁺ T cells demonstrated a highly activated, cytotoxic phenotype while simultaneously developing a canonical tissue-resident memory T cell (T_RM) transcriptional signature driven by interleukin-15 (IL-15)/IL-21 signaling. We found expression of a cluster of genes directly associated with tissue invasiveness, including those encoding adhesion molecules (ITGB2), specific chemokines (CCL3 and CCL4L1) and chemokine receptors (CD74), as well as multiple cytoskeletal proteins. This tissue invasion transcriptional signature was validated by its ability to discriminate the CD8⁺ T cell transcriptome of patients with GI aGVHD from those of GVHD-free patients. These results provide insights into the mechanisms controlling tissue occupancy of target organs by pathogenic donor CD8⁺ T_RM cells during aGVHD in primate transplant recipients.

Immunometabolic responses according to physical fitness status and lifelong exercise during aging: New roads for exercise immunology

Molecules such as cytokines, energetic substrates, and hormones found in the immune cell environment, especially lymphocytes and monocytes, are crucial for directing energy metabolism. In turn, changes in energy metabolism occur in a synchronized manner with the activation of certain signaling pathways, thereby this crosstalk is responsible for determining the functionality of immune cells. The immunometabolism field has grown over time and that is becoming increasingly promising in several populations; here we discuss the mechanisms involved in sedentary and physically active middle-aged individuals and master athletes. In this context, this review shows that the physical activity status and lifelong exercise seems to be good strategies for the promotion of metabolic and functional adaptations in T lymphocytes and monocytes, counteracting inflammatory environments caused by expanded adipose tissue and sedentary behavior, as well as delaying the immunosenescence caused by aging.

A phase 2 trial of the somatostatin analog pasireotide to prevent GI toxicity and acute GVHD in allogeneic hematopoietic stem cell transplant

Background

Allogeneic hematopoietic stem cell transplantation (HCT) is an often curative intent treatment, however it is associated with significant gastrointestinal (GI) toxicity and treatment related mortality. Graft-versus-host disease is a significant contributor to transplant-related mortality. We performed a phase 2 trial of the somatostatin analog pasireotide to prevent gastrointestinal toxicity and GVHD after myeloablative allogeneic HCT.

Methods

Patients received 0.9mg pasireotide every 12 hours from the day prior to conditioning through day +4 after HCT (or a maximum of 14 days). The primary outcomes were grade 3–4 gastrointestinal toxicity through day 30 and acute GVHD. Secondary outcomes were chronic GVHD, overall survival and relapse free survival at one year. Stool and blood samples were collected from before and after HCT for analyses of stool microbiome, local inflammatory markers, and systemic inflammatory and metabolic markers. Results were compared with matched controls.

Results

Twenty-six patients received pasireotide and were compared to 52 matched contemporaneous controls using a 1–2 match. Grade 3–4 GI toxicity occurred in 21 (81%) patients who received pasireotide and 35 (67%) controls (p = 0.33). Acute GVHD occurred in 15 (58%) patients in the pasireotide group and 28 (54%) controls (p = 0.94). Chronic GVHD occurred in 16 patients in the pasireotide group (64%) versus 22 patients in the control group (42%) (p = 0.12). Overall survival at 1 year in the pasireotide group was 63% (95% CI: 47%,86%) versus 82% (95% CI: 72%, 93%) in controls (log-rank p = 0.006). Relapse-free survival rate at one year was 40% (95% CI: 25%, 65%) in the pasireotide group versus 78% (95% CI: 68%, 91%) in controls (log-rank p = 0.002). After controlling for the effect of relevant covariates, patients in the pasireotide group had attenuated post-HCT loss of microbial diversity. Analysis of systemic inflammatory markers and metabolomics demonstrated feasibility of such analyses in patients undergoing allogeneic HCT. Baseline level and pre-to-post transplant changes in several inflammatory markers (including MIP1a, MIP1b, TNFa, IL8Pro, and IL6) correlated with likelihood of survival.

Conclusions

Pasireotide did not prevent gastrointestinal toxicity or acute GVHD compared to contemporaneous controls. Pasireotide was associated with numerically higher chronic GVHD and significantly decreased OS and RFS compared to contemporaneous controls. Pasireotide may provide a locally protective effect in the stool microbiome and in local inflammation as measured by stool calprotectin, stool beta-defensin, and stool diversity index.

Neither Donor nor Recipient Mitochondrial Haplotypes Are Associated with Unrelated Donor Transplant Outcomes: A Validation Study from the CIBMTR

Graft-versus-host-disease (GVHD) is a multistep process that involves T-cell recognition and priming toward alloantigen, expansion, acquisition of effector function, and repeated tissue injury, resulting in clinical manifestations of the disease. All of these processes have considerable metabolic demands and understanding the key role of mitochondria in cellular metabolism as it relates to GVHD has increased significantly. Mitochondrial DNA (mtDNA) haplotypes have been linked to functional differences in vitro, suggesting they have functional differences at an organismal level. We previously used mtDNA typing to assess the impact of mtDNA haplotypes on outcomes of ~400 allo-HCT patients. This pilot study identified uncommon mtDNA haplotypes potentially associated with inferior outcomes. We sought to validate pilot findings of associations between donor and recipient mitochondrial haplotypes and transplant outcome. We examined a cohort of 4143 donor-recipient pairs obtained from the Center for International Blood and Marrow Transplant Research. MtDNA was extracted from whole blood or peripheral blood mononuclear cells from donors and recipients and sequenced to discern haplotype. We used multiple regression analysis to examine the independent association of mtDNA haplotype with overall survival and grade III-IV acute GVHD (aGVHD) adjusting for known risk factors for poor transplant outcome. Neither recipient nor donor mtDNA haplotype reached groupwise significance for overall survival (P =.26 and .39, respectively) or grade III-IV aGVHD (P = .68 and.57, respectively). Adjustment for genomically determined ancestry in the subset of donor-recipient pairs for which this was available did not materially change results. We conclude that our original finding was due to chance in a small sample size and that there is essentially no evidence that mtDNA haplotype or haplotype mismatch contributes to risk of serious outcomes after allogeneic transplantation.

Immunometabolism in haematopoietic stem cell transplantation and adoptive cellular therapies

PURPOSE OF REVIEW

Controlling T cell activity through metabolic manipulation has become a prominent feature in immunology and practitioners of both adoptive cellular therapy (ACT) and haematopoietic stem cell transplantation (HSCT) have utilized metabolic interventions to control T cell function. This review will survey recent metabolic research efforts in HSCT and ACT to paint a broad picture of immunometabolism and highlight advances in each area.

RECENT FINDINGS

In HSCT, recent publications have focused on modifying reactive oxygen species, sirtuin signalling or the NAD salvage pathway within alloreactive T cells and regulatory T cells. In ACT, metabolic interventions that bolster memory T cell development, increase mitochondrial density and function, or block regulatory signals in the tumour microenvironment (TME) have recently been published.

SUMMARY

Metabolic interventions control immune responses. In ACT, efforts seek to improve the in-vivo metabolic fitness of T cells, while in HSCT energies have focused on blocking alloreactive T cell expansion or promoting regulatory T cells. Methods to identify new, metabolically targetable pathways, as well as the ability of metabolic biomarkers to predict disease onset and therapeutic response, will continue to advance the field towards clinically applicable interventions.

Endothelial cell and T-cell crosstalk: Targeting metabolism as a therapeutic approach in chronic inflammation

The role of metabolic reprogramming in the coordination of the immune response has gained increasing consideration in recent years. Indeed, it has become clear that changes in the metabolic status of immune cells can alter their functional properties. During inflammation, T cells need to generate sufficient energy and biomolecules to support growth, proliferation, and effector functions. Therefore, T cells need to rearrange their metabolism to meet these demands. A similar metabolic reprogramming has been described in endothelial cells, which have the ability to interact with and modulate the function of immune cells. In this overview, we will discuss recent insights in the complex crosstalk between endothelial cells and T cells as well as their metabolic reprogramming following activation. We highlight key components of this metabolic switch that can lead to the development of new therapeutics against chronic inflammatory disorders. LINKED ARTICLES: This article is part of a themed issue on Cellular metabolism and diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.10/issuetoc.

Targeting immune cell metabolism in kidney diseases

Insights into the relationship between immunometabolism and inflammation have enabled the targeting of several immunity-mediated inflammatory processes that underlie infectious diseases and cancer or drive transplant rejection, but this field remains largely unexplored in kidney diseases. The kidneys comprise heterogeneous cell populations, contain distinct microenvironments such as areas of hypoxia and hypersalinity, and are responsible for a functional triad of filtration, reabsorption and secretion. These distinctive features create myriad potential metabolic therapeutic targets in the kidney. Immune cells have crucial roles in the maintenance of kidney homeostasis and in the response to kidney injury, and their function is intricately connected to their metabolic properties. Changes in nutrient availability and biomolecules, such as cytokines, growth factors and hormones, initiate cellular signalling events that involve energy-sensing molecules and other metabolism-related proteins to coordinate immune cell differentiation, activation and function. Disruption of homeostasis promptly triggers the metabolic reorganization of kidney immune and non-immune cells, which can promote inflammation and tissue damage. The metabolic differences between kidney and immune cells offer an opportunity to specifically target immunometabolism in the kidney.

Metabolomic Signatures of Autoimmune Hepatitis in the Development of Cirrhosis

Objectives: Autoimmune hepatitis (AIH) can progress into severe outcomes, i.e., decompensated cirrhosis, from remarkable and persistent inflammation in the liver. Considering the energy-expending nature of inflammation, we tried to define the metabolomics signatures of AIH to uncover the underlying mechanisms of cirrhosis development and its metabolic biomarkers. Methods: Untargeted metabolomics analysis was performed on sera samples from 79 AIH patients at the stages (phenotypes) of non-cirrhosis (n = 27), compensated cirrhosis (n = 22), and decompensated cirrhosis (n = 30). Pattern recognition was used to find unique metabolite fingerprints of cirrhosis with or without decompensation. Results: Out of the 294 annotated metabolites identified, 2 metabolic fingerprints were found associated with the development of cirrhosis (independent of the decompensated state, 42 metabolites) and the evolution of decompensated cirrhosis (out of 47 metabolites), respectively. The cirrhosis-associated fingerprints (eigenmetabolite) showed better capability to differentiate cirrhosis from non-cirrhosis patients than the aminotransferase-to-platelet ratio index. From the metabolic fingerprints, we found two pairs of metabolites (Mesobilirubinogen/6-Hydroxynicotinic acid and LysoPA(8:0/0:0)/7alpha-Hydroxycholesterol) calculated as ratio of intensities, which revealed robust abilities to identify cirrhosis or predict decompensated patients, respectively. These phenotype-related fingerprint metabolites featured fundamental energy supply disturbance along with the development of AIH cirrhosis and progression to decompensation, which was characterized as increased lipolysis, enhanced proteolysis, and increased glycolysis. Conclusions: Remodeling of metabolism to meet the liver inflammation-related energy supply is one of the key signatures of AIH in the development of cirrhosis and decompensation. Therefore, drug regulation metabolism has great potential in the treatment of AIH.

Memory T Cells in Transplantation: Old Challenges Define New Directions

Immunologic memory is the ability of adaptive immune system to quickly and specifically recognize previously encountered antigens and initiate an effector response. Alloreactive memory cells can mount rapid and robust responses to the transplanted organ resulting in allograft injury. Thus preexisting humoral or cellular memory alloresponses are typically associated with poor graft outcomes in experimental and clinical transplantation. While both B and T lymphocytes exhibit memory responses, this review discusses recent updates on the biology of memory T cells and their relevance to the field of transplantation. Three major areas of focus are the emergence and characterization of tissue resident memory T cells, manipulation of T cell metabolic pathways, and the latest promising approaches to targeting detrimental T cell memory in the settings of organ transplantation.

Lysosomal Acid Lipase Is Required for Donor T Cells to Induce Graft-versus-Host Disease

Graft-versus-host disease (GVHD) limits the success of allogeneic hematopoietic cell transplantation (allo-HCT). Lysosomal acid lipase (LAL) mediates the intrinsic lipolysis of cells to generate free fatty acids (FFAs), which play an essential role in the development, proliferation, and function of T cells. Here, we find that LAL is essential for donor T cells to induce GVHD in murine models of allo-HCT. Specifically, LAL is required for donor T cell survival, differentiation, and alloreactivity in GVHD target organs, but not in lymphoid organs. LAL induces the differentiation of donor T cells toward GVHD pathogenic Th1/Tc1 and Th17 while suppressing regulatory T cell generation. LAL-/- T cells succumb to oxidative stress and become anergic in target organs. Pharmacologically targeting LAL effectively prevents GVHD development while preserving the GVL activity. Thus, the present study reveals the role of LAL in T cell alloresponse and pathogenicity and validates LAL as a target for controlling GVHD and tumor relapse after allo-HCT.

Why All the Fuss about Oxidative Phosphorylation (OXPHOS)?

Certain subtypes of cancer cells require oxidative phosphorylation (OXPHOS) to survive. Increased OXPHOS dependency is frequently a hallmark of cancer stem cells and cells resistant to chemotherapy and targeted therapies. Suppressing the OXPHOS function might also influence the tumor microenvironment by alleviating hypoxia and improving the antitumor immune response. Thus, targeting OXPHOS is a promising strategy to treat various cancers. A growing arsenal of therapeutic agents is under development to inhibit this biological process. This Perspective provides an overview of the structure and function of OXPHOS complexes, their biological functions in cancer, relevant research tools and models, as well as the limitations of OXPHOS as drug targets. We also focus on the current development status of OXPHOS inhibitors and potential therapeutic strategies to strengthen their clinical applications.

Natural products and other inhibitors of F1FO ATP synthase

F₁F_O ATP synthase is responsible for the production of >95% of all ATP synthesis within the cell. Dysregulation of its expression, activity or localization is linked to various human diseases including cancer, diabetes, and Alzheimer's and Parkinson's disease. In addition, ATP synthase is a novel and viable drug target for the development of antimicrobials as evidenced by bedaquiline, which was approved in 2012 for the treatment of tuberculosis. Historically, natural products have been a rich source of ATP synthase inhibitors that help unravel the role of F₁F_O ATP synthase in cellular bioenergetics. During the last decade, new modulators of ATP synthase have been discovered through the isolation of novel natural products as well as through a ligand-based drug design process. In addition, new data has been obtained with regards to the structure and function of ATP synthase under physiological and pathological conditions. Crystal structure studies have provided a significant insight into the rotary function of the enzyme and may provide additional opportunities to design a new generation of inhibitors. This review provides an update on recently discovered ATP synthase modulators as well as an update on existing scaffolds.

Metabolism of immune cells in cancer

Through the successes of checkpoint blockade and adoptive cellular therapy, immunotherapy has become an established treatment modality for cancer. Cellular metabolism has emerged as a critical determinant of the viability and function of both cancer cells and immune cells. In order to sustain prodigious anabolic needs, tumours employ a specialized metabolism that differs from untransformed somatic cells. This metabolism leads to a tumour microenvironment that is commonly acidic, hypoxic and/or depleted of critical nutrients required by immune cells. In this context, tumour metabolism itself is a checkpoint that can limit immune-mediated tumour destruction. Because our understanding of immune cell metabolism and cancer metabolism has grown significantly in the past decade, we are on the cusp of being able to unravel the interaction of cancer cell metabolism and immune metabolism in therapeutically meaningful ways. Although there are metabolic processes that are seemingly fundamental to both cancer and responding immune cells, metabolic heterogeneity and plasticity may serve to distinguish the two. As such, understanding the differential metabolic requirements of the diverse cells that comprise an immune response to cancer offers an opportunity to selectively regulate immune cell function. Such a nuanced evaluation of cancer and immune metabolism can uncover metabolic vulnerabilities and therapeutic windows upon which to intervene for enhanced immunotherapy.

Metabolic Pathways in Alloreactive T Cells

Allogeneic hematopoietic stem cell transplantation (aHSCT) is a curative therapy for a range of hematologic illnesses including aplastic anemia, sickle cell disease, immunodeficiency, and high-risk leukemia, but the efficacy of aHSCT is often undermined by graft-versus-host disease (GVHD), where T cells from the donor attack and destroy recipient tissues. Given the strong interconnection between T cell metabolism and cellular function, determining the metabolic pathways utilized by alloreactive T cells is fundamental to deepening our understanding of GVHD biology, including its initiation, propagation, and potential mitigation. This review summarizes the metabolic pathways available to alloreactive T cells and highlights key metabolic proteins and pathways linking T cell metabolism to effector function. Our current knowledge of alloreactive T cell metabolism is then explored, showing support for glycolysis, fat oxidation, and glutamine metabolism but also offering a potential explanation for how these presumably contradictory metabolic findings might be reconciled. Examples of additional ways in which metabolism impacts aHSCT are addressed, including the influence of butyrate metabolism on GVHD resolution. Finally, the caveats and challenges of assigning causality using our current metabolic toolbox is discussed, as well as likely future directions in immunometabolism, both to highlight the strengths of the current evidence as well as recognize some of its limitations.

Photodepletion with 2-Se-Cl prevents lethal graft-versus-host disease while preserving antitumor immunity

Acute graft-versus-host-disease (GVHD), limits the use of hematopoietic cell transplant (HCT) to treat a variety of malignancies. Any new therapeutic approach must satisfy three requirements: 1) Prevent GVHD, 2) Maintain anti-pathogen immunity, and 3) Maintain anti-tumor immunity. In prior studies we have shown that the selective photosensitizer 2-Se-Cl eliminates highly alloreactive lymphocytes from the graft prior to HCT preventing GVHD and that antiviral immune responses were preserved following incubation with 2-Se-Cl. In this report, we investigated whether 2-Se-Cl treatment preserves antitumor immunity, and then used high dimensional flow cytometry to identify the determinants of successful immune reconstitution. Donor C57BL/6 splenocytes were cocultured for 4 days with irradiated BALB/c splenocytes and then exposed to 2-Se-Cl. Photodepletion (PD)-treated splenocytes were then infused into lethally irradiated BALB/c mice inoculated with A20 leukemia/lymphoma cells. Recipient mice that received PD-treated splenocytes survived > 100 days without evidence of GVHD or leukemia. In contrast, mice that did not receive PD-treated cells at time of HCT died of leukemia progression. Multiparameter flow cytometry of cytokines and surface markers on peripheral blood samples 15 days after HCT demonstrated unique patterns of immune reconstitution. We found that before clinical disease onset GVHD was marked by functionally exhausted T cells, while tumor clearance and long-term survival were associated with an expansion of polyfunctional T cells, monocytes, and DCs early after transplantation. Taken together these results demonstrate that 2-Se-Cl photodepletion is a new treatment that can facilitate HCT by preventing GVHD while preserving antiviral and anti-tumor immunity.

Exploiting immunometabolism and T cell function for solid organ transplantation

Cellular metabolism is central to T cell function and proliferation, with most of the research to date focusing on cancer and autoimmunity. Cellular metabolism is associated with a host of physiological phenomena, from epigenetic changes, to cellular function and fate. For the purpose of this review, we will discuss the metabolism of T cells relating to their differentiation and function. We will cover a variety of metabolic processes, ranging from glycolysis to amino acid metabolism. Understanding how T cell metabolism informs T cell function may be useful to understand alloimmune responses and design novel therapies to improve graft outcome.

Glutathione dynamics determine the therapeutic efficacy of mesenchymal stem cells for graft-versus-host disease via CREB1-NRF2 pathway

Glutathione (GSH), the most abundant nonprotein thiol functioning as an antioxidant, plays critical roles in maintaining the core functions of mesenchymal stem cells (MSCs), which are used as a cellular immunotherapy for graft-versus-host disease (GVHD). However, the role of GSH dynamics in MSCs remains elusive. Genome-wide gene expression profiling and high-throughput live-cell imaging assays revealed that CREB1 enforced the GSH-recovering capacity (GRC) of MSCs through NRF2 by directly up-regulating NRF2 target genes responsible for GSH synthesis and redox cycling. MSCs with enhanced GSH levels and GRC mediated by CREB1-NRF2 have improved self-renewal, migratory, anti-inflammatory, and T cell suppression capacities. Administration of MSCs overexpressing CREB1-NRF2 target genes alleviated GVHD in a humanized mouse model, resulting in improved survival, decreased weight loss, and reduced histopathologic damages in GVHD target organs. Collectively, these findings demonstrate the molecular and functional importance of the CREB1-NRF2 pathway in maintaining MSC GSH dynamics, determining therapeutic outcomes for GVHD treatment.

Combination of host immune metabolic biomarkers for the PD-1 blockade cancer immunotherapy

BACKGROUNDCurrent clinical biomarkers for the programmed cell death 1 (PD-1) blockade therapy are insufficient because they rely only on the tumor properties, such as programmed cell death ligand 1 expression frequency and tumor mutation burden. Identifying reliable, responsive biomarkers based on the host immunity is necessary to improve the predictive values.METHODSWe investigated levels of plasma metabolites and T cell properties, including energy metabolism markers, in the blood of patients with non-small cell lung cancer before and after treatment with nivolumab (n = 55). Predictive values of combination markers statistically selected were evaluated by cross-validation and linear discriminant analysis on discovery and validation cohorts, respectively. Correlation between plasma metabolites and T cell markers was investigated.RESULTSThe 4 metabolites derived from the microbiome (hippuric acid), fatty acid oxidation (butyrylcarnitine), and redox (cystine and glutathione disulfide) provided high response probability (AUC = 0.91). Similarly, a combination of 4 T cell markers, those related to mitochondrial activation (PPARγ coactivator 1 expression and ROS), and the frequencies of CD8+PD-1hi and CD4+ T cells demonstrated even higher prediction value (AUC = 0.96). Among the pool of selected markers, the 4 T cell markers were exclusively selected as the highest predictive combination, probably because of their linkage to the abovementioned metabolite markers. In a prospective validation set (n = 24), these 4 cellular markers showed a high accuracy rate for clinical responses of patients (AUC = 0.92).CONCLUSIONCombination of biomarkers reflecting host immune activity is quite valuable for responder prediction.FUNDINGAMED under grant numbers 18cm0106302h0003, 18gm0710012h0105, and 18lk1403006h0002; the Tang Prize Foundation; and JSPS KAKENHI grant numbers JP16H06149, 17K19593, and 19K17673.

Targeting NAD immunometabolism limits severe graft-versus-host disease and has potent antileukemic activity

Acute graft-versus-host disease (aGVHD) and tumor relapse remain major complications after allogeneic hematopoietic stem cell transplantation. Alloreactive T cells and cancer cells share a similar metabolic phenotype to meet the bioenergetic demands necessary for cellular proliferation and effector functions. Nicotinamide adenine dinucleotide (NAD) is an essential co-factor in energy metabolism and is constantly replenished by nicotinamide phosphoribosyl-transferase (Nampt), the rate-limiting enzyme in the NAD salvage pathway. Here we show, that Nampt blockage strongly ameliorates aGVHD and limits leukemic expansion. Nampt was highly elevated in serum of patients with gastrointestinal GVHD and was particularly abundant in human and mouse intestinal T cells. Therapeutic application of the Nampt small-molecule inhibitor, Fk866, strongly attenuated experimental GVHD and caused NAD depletion in T-cell subsets, which displayed differential susceptibility to NAD shortage. Fk866 robustly inhibited expansion of alloreactive but not memory T cells and promoted FoxP3-mediated lineage stability in regulatory T cells. Furthermore, Fk866 strongly reduced the tumor burden in mouse leukemia and graft-versus-leukemia models. Ex vivo studies using lymphocytes from GVHD patients demonstrated potent antiproliferative properties of Fk866, suggesting potential clinical utility. Thus, targeting NAD immunometabolism represents a novel approach to selectively inhibit alloreactive T cells during aGVHD with additional antileukemic efficacy.

The Untapped Opportunity and Challenge of Immunometabolism: A New Paradigm for Drug Discovery

Here, we explore the manipulation of immune cell metabolism as a strategy in target discovery and drug development for immune-mediated diseases. Comparing exploitation of metabolic pathways to kill tumor cells for cancer treatment with the reprogramming of immune cells to treat autoimmune diseases highlights differences that confer several advantages to the latter (including a more favorable therapeutic index and greater target stability). We discuss technological capabilities and gaps, including the challenge of relating in vitro observations to in vivo biology. Finally, we conclude by identifying future opportunities that will move the field forward and accelerate drug discovery.

Distinct Regulatory and Effector T Cell Metabolic Demands during Graft-Versus-Host Disease

Despite graft-versus-host disease (GVHD) prophylactic agents, the success and wider utilization of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is limited by GVHD. Increasing donor graft regulatory T cell (Treg):effector T cell (Teff) ratios can substantially reduce GVHD in cancer patients, but pre-HSCT conditioning regimens and GVHD create a challenging inflammatory environment for Treg stability, persistence, and function. Metabolism plays a crucial role in T cell and Treg differentiation, and development of effector function. Although glycolysis is a main driver of allogeneic T cell-driven GVHD, oxidative phosphorylation is a main driver of Treg suppressor function. This review focuses on recent advances in our understanding of Treg metabolism in the context of GVHD, and discusses potential therapeutic applications of Tregs in the prevention or treatment of GVHD in cancer patients.

Glucocorticoid resistance of allogeneic T cells alters the gene expression profile in the inflamed small intestine of mice suffering from acute graft-versus-host disease

Glucocorticoids (GCs) play an important role in controlling acute graft-versus-host disease (aGvHD), a frequent complication of allogeneic hematopoietic stem cell transplantation. The anti-inflammatory activity of GCs is mainly ascribed to the modulation of T cells and macrophages, for which reason a genetically induced GC resistance of either of these cell types causes aggravated aGvHD. Since only a few genes are currently known that are differentially regulated under these conditions, we analyzed the expression of 54 candidate genes in the inflamed small intestine of mice suffering from aGvHD when either allogeneic T cells or host myeloid cells were GC resistant using a microfluidic dynamic array platform for high-throughput quantitative PCR. The majority of genes categorized as cytokines (e.g. Il2, Il6), chemokines (e.g. Ccl2, Cxcl1), cell surface receptors (e.g. Fasl, Ctla4) and intracellular molecules (e.g. Dusp1, Arg1) were upregulated in mice transplanted with GC resistant allogeneic T cells. Moreover, the expression of several genes linked to energy metabolism (e.g. Glut1) was altered. Surprisingly, mice harboring GC resistant myeloid cells showed almost no changes in gene expression despite their fatal disease course after aGvHD induction. To identify additional genes in the inflamed small intestine that were affected by a GC resistance of allogeneic T cells, we performed an RNAseq analysis, which uncovered more than 500 differentially expressed transcripts (e.g. Cxcr6, Glut3, Otc, Aoc1, Il1r1, Sphk1) that were enriched for biological processes associated with inflammation and tissue disassembly. The changes in gene expression could be confirmed during full-blown disease but hardly any of them in the preclinical phase using high-throughput quantitative PCR. Further analysis of some of these genes revealed a highly selective expression pattern in T cells, intestinal epithelial cells and macrophages, which correlated with their regulation during disease progression. Collectively, we identified an altered gene expression profile caused by GC resistance of transplanted allogeneic T cells, which could help to define new targets for aGvHD therapy.

Donor and host B7-H4 expression negatively regulates acute graft-versus-host disease lethality

B7-H4 is a negative regulatory B7 family member. We investigated the role of host and donor B7-H4 in regulating acute graft-versus-host disease (GVHD). Allogeneic donor T cells infused into B7-H4-/- versus WT recipients markedly accelerated GVHD-induced lethality. Chimera studies pointed toward B7-H4 expression on host hematopoietic cells as more critical than parenchymal cells in controlling GVHD. Rapid mortality in B7-H4-/- recipients was associated with increased donor T cell expansion, gut T cell homing and loss of intestinal epithelial integrity, increased T effector function (proliferation, proinflammatory cytokines, cytolytic molecules), and reduced apoptosis. Higher metabolic demands of rapidly proliferating donor T cells in B7-H4-/- versus WT recipients required multiple metabolic pathways, increased extracellular acidification rates (ECARs) and oxygen consumption rates (OCRs), and increased expression of fuel substrate transporters. During GVHD, B7-H4 expression was upregulated on allogeneic WT donor T cells. B7-H4-/- donor T cells given to WT recipients increased GVHD mortality and had function and biological properties similar to WT T cells from allogeneic B7-H4-/- recipients. Graft-versus-leukemia responses were intact regardless as to whether B7-H4-/- mice were used as hosts or donors. Taken together, these data provide new insights into the negative regulatory processes that control GVHD and provide support for developing therapeutic strategies directed toward the B7-H4 pathway.

Targeting T Cell Metabolism in Inflammatory Skin Disease

A properly functioning T cell compartment is crucial to protect the host from infections, tumors, and environmental substances. In recent years, it has become increasingly clear that the processes underlying proper T cell activation, proliferation, and differentiation require well-tuned and dynamic changes in T cell metabolism. Thus, proper metabolic reprogramming in T cells is crucial to ensure proper immunity in the context of infection and anti-tumor immunity. Conversely, aberrant regulation of T cell metabolism can impair T cell function and thereby contribute to T cell-mediated disease. In this review, the relevance of recent insights into T cell metabolism for prototypical T cell-mediated skin diseases will be discussed and their therapeutic potential will be outlined. First, the major modules of T cell metabolism are summarized. Then, the importance of T cell metabolism for T cell-mediated skin diseases such as psoriasis and allergic contact dermatitis is discussed, based on the current state of our understanding thereof. Finally, novel therapeutic opportunities for inflammatory skin disease that might emerge from investigations in T cell metabolism are outlined.

Targeting metabolism to regulate immune responses in autoimmunity and cancer

Metabolic programming is emerging as a critical mechanism to alter immune cell activation, differentiation and function. Targeting metabolism does not completely suppress or activate the immune system but selectively regulates immune responses. The different metabolic requirements of the diverse cells that constitute an immune response provide a unique opportunity to separate effector functions from regulatory functions. Likewise, cells can be metabolically reprogrammed to promote either their short-term effector functions or long-term memory capacity. Studies in the growing field of immunometabolism support a paradigm of 'cellular selectivity based on demand', in which generic inhibitors of ubiquitous metabolic processes selectively affect cells with the greatest metabolic demand and have few effects on other cells of the body. Targeting metabolism, rather than particular cell types or cytokines, in metabolically demanding processes such as autoimmunity, graft rejection, cancer and uncontrolled inflammation could lead to successful strategies in controlling the pathogenesis of these complex disorders.

Thioredoxin-1 confines T cell alloresponse and pathogenicity in graft-versus-host disease

Oxidative stress is elevated in the recipients of allogeneic hematopoietic transplantation (allo-HCT) and likely contributes to the development of graft-versus-host disease (GVHD). GVHD is characterized by activation, expansion, cytokine production and migration of alloreactive donor T cells, and remains a major cause of morbidity and mortality after allo-HCT. Hence, strategies to limit oxidative stress in GVHD are highly desirable. Thioredoxin1 (Trx1) counteracts oxidative stress by scavenging reactive oxygen species (ROS) and regulating other enzymes that metabolize H2O2. The present study sought to elucidate the role of Trx1 in the pathophysiology of GVHD. Using murine and xenograft models of allogeneic bone marrow transplantation (allo-BMT) and genetic (human Trx1-transgenic, Trx1-Tg) as well as pharmacologic (human recombinant Trx1, RTrx1) strategies; we found that Trx1-Tg donor T cells or administration of the recipients with RTrx1 significantly reduced GVHD severity. Mechanistically, we observed RTrx1 reduced ROS accumulation and cytokine production of mouse and human T cells in response to alloantigen stimulation in vitro. In allo-BMT settings, we found that Trx1-Tg or RTrx1 decreased downstream signaling molecules including NFκB activation and T-bet expression, and reduced proliferation, IFN-γ production and ROS accumulation in donor T cells within GVHD target organs. More importantly, administration of RTrx1 did not impair the graft-versus-leukemia (GVL) effect. Taken together, the current work provides a strong rationale and demonstrates feasibility to target the ROS pathway, which can be readily translated into clinic.