Adenosine A2A receptor activation reduces hepatic ischemia reperfusion injury by inhibiting CD1d-dependent NKT cell activation

Diverse NKT cells regulate early inflammation and neurological outcomes after cardiac arrest and resuscitation

Neurological injury drives most deaths and morbidity among patients hospitalized for out-of-hospital cardiac arrest (OHCA). Despite its clinical importance, there are no effective pharmacological therapies targeting post-cardiac arrest (CA) neurological injury. Here, we analyzed circulating immune cells from a large cohort of patients with OHCA, finding that lymphopenia independently associated with poor neurological outcomes. Single-cell RNA sequencing of immune cells showed that T cells with features of both innate T cells and natural killer (NK) cells were increased in patients with favorable neurological outcomes. We more specifically identified an early increase in circulating diverse NKT (dNKT) cells in a separate cohort of patients with OHCA who had good neurological outcomes. These cells harbored a diverse T cell receptor repertoire but were consistently specific for sulfatide antigen. In mice, we found that sulfatide-specific dNKT cells trafficked to the brain after CA and resuscitation. In the brains of mice lacking NKT cells (Cd1d-/-), we observed increased inflammatory chemokine and cytokine expression and accumulation of macrophages when compared with wild-type mice. Cd1d-/- mice also had increased neuronal injury, neurological dysfunction, and worse mortality after CA. To therapeutically enhance dNKT cell activity, we treated mice with sulfatide lipid after CA, showing that it improved neurological function. Together, these data show that sulfatide-specific dNKT cells are associated with good neurological outcomes after clinical OHCA and are neuroprotective in mice after CA. Strategies to enhance the number or function of dNKT cells may thus represent a treatment approach for CA.

Bioinformatics-based analysis of the role of immune-related genes in acute rejection after kidney transplantation and renal cancer development

Acute rejection (AR) is a common complication in the early stage after kidney transplantation. Some studies have shown that the occurrence of AR after kidney transplantation may further affect the development of tumors, and both AR and tumor development are related to immune cells and immune genes, so it is particularly important to diagnose the occurrence of AR at an early stage and to analyze the correlation between AR and tumors. In this study, we applied bioinformatics techniques for differential expression analysis and weighted gene co-expression network analysis analysis of AR patients to obtain differentially expressed genes and modular genes significantly associated with AR, respectively, so as to obtain their intersecting genes with immune-related genes; 21 intersecting genes were screened by lasso regression and Boruta algorithm to obtain the genes, and finally, the feature genes that were significantly associated with the dependent variable were further obtained by single-factor and multi-factor logistic regression. Then the best diagnostic model for AR was screened by 10 machine learning methods, and we evaluated the model in various aspects, such as receiver operator characteristic curve, decision curve analysis. We then focused on the role of FAM3C in renal cancer. We finally screened 4 feature genes (CD1D, FPR2, FAM3C, and HMOX1) to construct the AR diagnostic model; through comparative evaluation, we believe that logistic regression shows a better advantage in the construction of diagnostic models for AR. FAM3C may become a potential biological marker for AR diagnosis and plays an important role in the development of renal cancer. In summary, immune-related genes play an important role in the diagnosis of AR after kidney transplantation, and the gene FAM3C may be a potential therapeutic target for AR and renal cancer.

Role of G protein coupled receptors in acute kidney injury

Acute kidney injury (AKI) is a clinical condition characterized by a rapid decline in kidney function, which is associated with local inflammation and programmed cell death in the kidney. The G protein-coupled receptors (GPCRs) represent the largest family of signaling transduction proteins in the body, and approximately 40% of drugs on the market target GPCRs. The expressions of various GPCRs, prostaglandin receptors and purinergic receptors, to name a few, are significantly altered in AKI models. And the role of GPCRs in AKI is catching the eyes of researchers due to their distinctive biological functions, such as regulation of hemodynamics, metabolic reprogramming, and inflammation. Therefore, in this review, we aim to discuss the role of GPCRs in the pathogenesis of AKI and summarize the relevant clinical trials involving GPCRs to assess the potential of GPCRs and their ligands as therapeutic targets in AKI and the transition to AKI-CKD.

Ectonucleotidases in Ischemia Reperfusion Injury: Unravelling the Interplay With Mitochondrial Dysfunction in Liver Transplantation

Ischemia-reperfusion injury (IRI) profoundly impacts organ transplantation, especially in orthotopic liver transplantation (OLT). Disruption of the mitochondrial respiratory chain during ischemia leads to ATP loss and ROS production. Reperfusion exacerbates mitochondrial damage, triggering the release of damage-associated molecular patterns (DAMPs) and inflammatory responses. Mitochondrial dysfunction, a pivotal aspect of IRI, is explored in the context of the regulatory role of ectonucleotidases in purinergic signaling and immune responses. CD39, by hydrolyzing ATP and ADP; and CD73, by converting AMP to adenosine, emerge as key players in mitigating liver IRI, particularly through ischemic preconditioning and adenosine receptor signaling. Despite established roles in vascular health and immunity, the impact of ectonucleotidases on mitochondrial function during hepatic IRI is unclear. This review aims to elucidate the interplay between CD39/73 and mitochondria, emphasizing their potential as therapeutic targets for liver transplantation. This article explores the role of CD39/73 in tissue hypoxia, emphasizing adenosine production during inflammation. CD39 and CD73 upregulation under hypoxic conditions regulate immune responses, demonstrating protective effects in various organ-specific ischemic models. However, prolonged adenosine activation may have dual effects, beneficial in acute settings but detrimental in chronic hypoxia. Herein, we raise questions about ectonucleotidases influencing mitochondrial function during hepatic IRI, drawing parallels with cancer cell responses to chemotherapy. The review underscores the need for comprehensive research into the intricate interplay between ectonucleotidases, mitochondrial dynamics, and their therapeutic implications in hepatic IRI, providing valuable insights for advancing transplantation outcomes.

Adenosine-mediated immune responses in inflammatory bowel disease

Extracellular ATP and its derivates mediate a signaling pathway that might be pharmacologically targeted to treat inflammatory conditions. Extracellular adenosine, the product of ATP hydrolysis by ectonucleotidase enzymes, plays a key role in halting inflammation while promoting immune tolerance. The rate-limiting ectoenzyme ENTPD1/CD39 and the ecto-5'-nucleotidase/CD73 are the prototype members of the ectonucleotidase family, being responsible for ATP degradation into immunosuppressive adenosine. The biological effects of adenosine are mediated via adenosine receptors, a family of G protein-coupled receptors largely expressed on immune cells where they modulate innate and adaptive immune responses. Inflammatory bowel disease (IBD) is a serious inflammatory condition of the gastrointestinal tract, associated with substantial morbidity and often refractory to currently available medications. IBD is linked to altered interactions between the gut microbiota and the immune system in genetically predisposed individuals. A wealth of studies conducted in patients and animal models highlighted the role of various adenosine receptors in the modulation of chronic inflammatory diseases like IBD. In this review, we will discuss the most recent findings on adenosine-mediated immune responses in different cell types, with a focus on IBD and its most common manifestations, Crohn's disease and ulcerative colitis.

invariant Natural Killer T cell therapy as a novel therapeutic approach in hematological malignancies

Invariant Natural Killer T cell therapy is an emerging platform of immunotherapy for cancer treatment. This unique cell population is a promising candidate for cell therapy for cancer treatment because of its inherent cytotoxicity against CD1d positive cancers as well as its ability to induce host CD8 T cell cross priming. Substantial evidence supports that iNKT cells can modulate myelomonocytic populations in the tumor microenvironment to ameliorate immune dysregulation to antagonize tumor progression. iNKT cells can also protect from graft-versus-host disease (GVHD) through several mechanisms, including the expansion of regulatory T cells (Treg). Ultimately, iNKT cell-based therapy can retain antitumor activity while providing protection against GVHD simultaneously. Therefore, these biological properties render iNKT cells as a promising "off-the-shelf" therapy for diverse hematological malignancies and possible solid tumors. Further the introduction of a chimeric antigen recetor (CAR) can further target iNKT cells and enhance function. We foresee that improved vector design and other strategies such as combinatorial treatments with small molecules or immune checkpoint inhibitors could improve CAR iNKT in vivo persistence, functionality and leverage anti-tumor activity along with the abatement of iNKT cell dysfunction or exhaustion.

The immune system in neurological diseases: What innate-like T cells have to say

The immune system classically consists of 2 lines of defense, innate and adaptive, both of which interact with one another effectively to protect us against any pathogenic threats. Importantly, there is a diverse subset of cells known as innate-like T cells that act as a bridge between the innate and adaptive immune systems and are pivotal players in eliciting inflammatory immune responses. A growing body of evidence has demonstrated the regulatory impact of these innate-like T cells in central nervous system (CNS) diseases and that such immune cells can traffic into the brain in multiple pathological conditions, which can be typically attributed to the breakdown of the blood-brain barrier. However, until now, it has been poorly understood whether innate-like T cells have direct protective or causative properties, particularly in CNS diseases. Therefore, in this review, our attention is focused on discussing the critical roles of 3 unique subsets of unconventional T cells, namely, natural killer T cells, γδ T cells, and mucosal-associated invariant T cells, in the context of CNS diseases, disorders, and injuries and how the interplay of these immune cells modulates CNS pathology, in an attempt to gain a better understanding of their complex functions.

Circadian Influences on Myocardial Ischemia-Reperfusion Injury and Heart Failure

The impact of circadian rhythms on cardiovascular function and disease development is well established, with numerous studies in genetically modified animals emphasizing the circadian molecular clock's significance in the pathogenesis and pathophysiology of myocardial ischemia and heart failure progression. However, translational preclinical studies targeting the heart's circadian biology are just now emerging and are leading to the development of a novel field of medicine termed circadian medicine. In this review, we explore circadian molecular mechanisms and novel therapies, including (1) intense light, (2) small molecules modulating the circadian mechanism, and (3) chronotherapies such as cardiovascular drugs and meal timings. These promise significant clinical translation in circadian medicine for cardiovascular disease. (4) Additionally, we address the differential functioning of the circadian mechanism in males versus females, emphasizing the consideration of biological sex, gender, and aging in circadian therapies for cardiovascular disease.

The role of natural killer T cells in liver transplantation

Natural killer T cells (NKTs) are innate-like lymphocytes that are abundant in the liver and participate in liver immunity. NKT cells express both NK cell and T cell markers, modulate innate and adaptive immune responses. Type I and Type II NKT cells are classified according to the TCR usage, while they recognize lipid antigen in a non-classical major histocompatibility (MHC) molecule CD1d-restricted manner. Once activated, NKT cells can quickly produce cytokines and chemokines to negatively or positively regulate the immune responses, depending on the different NKT subsets. In liver transplantation (LTx), the immune reactions in a series of processes determine the recipients' long-term survival, including ischemia-reperfusion injury, alloresponse, and post-transplant infection. This review provides insight into the research on NKT cells subpopulations in LTx immunity during different processes, and discusses the shortcomings of the current research on NKT cells. Additionally, the CD56-expressing T cells are recognized as a NK-like T cell population, they were also discussed during these processes.

Adenosinergic metabolism pathway: an emerging target for improving outcomes of solid organ transplantation

Extracellular nucleotides are widely recognized as crucial modulators of immune responses in peripheral tissues. Adenosine triphosphate (ATP) and adenosine are key components of extracellular nucleotides, the balance of which contributes to immune homeostasis. Under tissue injury, ATP exerts its pro-inflammatory function, while the adenosinergic pathway rapidly degrades ATP to immunosuppressive adenosine, thus inhibiting excessive and uncontrolled inflammatory responses. Previous reviews have explored the immunoregulatory role of extracellular adenosine in various pathological conditions, especially inflammation and malignancy. However, current knowledge regarding adenosine and adenosinergic metabolism in the context of solid organ transplantation remains fragmented. In this review, we summarize the latest information on adenosine metabolism and the mechanisms by which it suppresses the effector function of immune cells, as well as highlight the protective role of adenosine in all stages of solid organ transplantation, including reducing ischemia reperfusion injury during organ procurement, alleviating rejection, and promoting graft regeneration after transplantation. Finally, we discuss the potential for future clinical translation of adenosinergic pathway in solid organ transplantation.

Classification of regulatory T cells and their role in myocardial ischemia-reperfusion injury

Myocardial ischemia-reperfusion injury (MIRI) is closely related to the final infarct size in acute myocardial infarction (AMI). Therefore, reducing MIRI can effectively improve the prognosis of AMI patients. At the same time, the healing process after AMI is closely related to the local inflammatory microenvironment. Regulatory T cells (Tregs) can regulate various physiological and pathological immune inflammatory responses and play an important role in regulating the immune inflammatory response after AMI. However, different subtypes of Tregs have different effects on MIRI, and the same subtype of Tregs may also have different effects at different stages of MIRI. This article systematically reviews the classification and function of Tregs, as well as the role of various subtypes of Tregs in MIRI. A comprehensive understanding of the role of each subtype of Tregs can help design effective methods to control immune reactions, reduce MIRI, and provide new potential therapeutic options for AMI.

Adenosine A2A receptor is a tumor suppressor of NASH-associated hepatocellular carcinoma

Inhibition of adenosine A2A receptor (A2AR) is a promising approach for cancer immunotherapy currently evaluated in several clinical trials. We here report that anti-obesogenic and anti-inflammatory functions of A2AR, however, significantly restrain hepatocellular carcinoma (HCC) development. Adora2a deletion in mice triggers obesity, non-alcoholic steatohepatitis (NASH), and systemic inflammation, leading to spontaneous HCC and promoting dimethylbenzyl-anthracene (DMBA)- or diethylnitrosamine (DEN)-induced HCC. Conditional Adora2a deletion reveals critical roles of myeloid and hepatocyte-derived A2AR signaling in restraining HCC by limiting hepatic inflammation and steatosis. Remarkably, the impact of A2AR pharmacological blockade on HCC development is dependent on pre-existing NASH. In support of our animal studies, low ADORA2A gene expression in human HCC is associated with cirrhosis, hepatic inflammation, and poor survival. Together, our study uncovers a previously unappreciated tumor-suppressive function for A2AR in the liver and suggests caution in the use of A2AR antagonists in patients with NASH and NASH-associated HCC.

Efficacy of Invariant Natural Killer T Cell Infusion Plus Transarterial Embolization vs Transarterial Embolization Alone for Hepatocellular Carcinoma Patients: A Phase 2 Randomized Clinical Trial

Purpose

Invariant NKT cells (iNKT) are CD1d-restricted T cells with the capacity of antitumor immunity. The safety of autologous iNKT cell treatment in hepatocellular carcinoma (HCC) has been verified. This study aimed to investigate its efficacy in advanced HCC after transarterial chemoembolization (TACE) failure.

Patients and methods

This open-label, randomized, controlled, trial enrolled 60 patients with unresectable HCC after TACE failure at three centers. Transarterial embolization (TAE) was used instead of TACE to protect iNKT cell function. Patients were randomly assigned (1:1) to receive TAE therapy with (TAE-iNKT) or without (TAE) biweekly iNKT cell infusion. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall survival (OS), objective response rate (ORR), disease control rate (DCR), quality of life (QoL), peripheral blood cell count, and safety.

Results

Fifty-four patients completed the study. Median PFS was significantly higher in TAE-iNKT patients (5.7 months [95% CI, 4.3-7.0 months]) compared with TAE patients (2.7 months [95% CI, 2.3-3.2 months]; hazard ratio 0.32 [95% CI, 0.16-0.63]; P<0.001). Higher ORR and DCR were observed in TAE-iNKT patients (52% and 85%, respectively) compared with TAE patients (11% and 33%; respectively). Five TAE-iNKT patients and 1 TAE patient achieved completed response. The median time to deterioration in QoL was longer in TAE-iNKT patients (9.2 months [95% CI, 6.0-13.3 months]) compared with TAE patients (3.0 months [95% CI, 2.9-3.0 months]). The mean lymphocytes were higher in the TAE-iNKT group than in the TAE group at 8 (1.48 vs 0.95×109/L, P = 0.007) and 12 (1.49 vs 0.89×109/L, P = 0.001) weeks. Grade 3 adverse events occurred in 1 TAE-iNKT patient (4%) and 5 TAE patients (19%). All the other adverse events were grade 1-2.

Conclusion

iNKT cell infusion significantly improved PFS, ORR, DCR, and QoL with manageable toxicity during TAE therapy in patients with HCC. Trial Registration ClinicalTrials.gov Identifier: NCT04011033.

Regadenoson for the treatment of COVID-19: A five case clinical series and mouse studies

BACKGROUND

Adenosine inhibits the activation of most immune cells and platelets. Selective adenosine A2A receptor (A2AR) agonists such as regadenoson (RA) reduce inflammation in most tissues, including lungs injured by hypoxia, ischemia, transplantation, or sickle cell anemia, principally by suppressing the activation of invariant natural killer T (iNKT) cells. The anti-inflammatory effects of RA are magnified in injured tissues due to induction in immune cells of A2ARs and ecto-enzymes CD39 and CD73 that convert ATP to adenosine in the extracellular space. Here we describe the results of a five patient study designed to evaluate RA safety and to seek evidence of reduced cytokine storm in hospitalized COVID-19 patients.

METHODS AND FINDINGS

Five COVID-19 patients requiring supplemental oxygen but not intubation (WHO stages 4-5) were infused IV with a loading RA dose of 5 μg/kg/h for 0.5 h followed by a maintenance dose of 1.44 μg/kg/h for 6 hours, Vital signs and arterial oxygen saturation were recorded, and blood samples were collected before, during and after RA infusion for analysis of CRP, D-dimer, circulating iNKT cell activation state and plasma levels of 13 proinflammatory cytokines. RA was devoid of serious side effects, and within 24 hours from the start of infusion was associated with increased oxygen saturation (93.8 ± 0.58 vs 96.6 ± 1.08%, P<0.05), decreased D-dimer (754 ± 17 vs 518 ± 98 ng/ml, P<0.05), and a trend toward decreased CRP (3.80 ± 1.40 vs 1.98 ± 0.74 mg/dL, P = 0.075). Circulating iNKT cells, but not conventional T cells, were highly activated in COVID-19 patients (65% vs 5% CD69+). RA infusion for 30 minutes reduced iNKT cell activation by 50% (P<0.01). RA infusion for 30 minutes did not influence plasma cytokines, but infusion for 4.5 or 24 hours reduced levels of 11 of 13 proinflammatory cytokines. In separate mouse studies, subcutaneous RA infusion from Alzet minipumps at 1.44 μg/kg/h increased 10-day survival of SARS-CoV-2-infected K18-hACE2 mice from 10 to 40% (P<0.001).

CONCLUSIONS

Infused RA is safe and produces rapid anti-inflammatory effects mediated by A2A adenosine receptors on iNKT cells and possibly in part by A2ARs on other immune cells and platelets. We speculate that iNKT cells are activated by release of injury-induced glycolipid antigens and/or alarmins such as IL-33 derived from virally infected type II epithelial cells which in turn activate iNKT cells and secondarily other immune cells. Adenosine released from hypoxic tissues, or RA infused as an anti-inflammatory agent decrease proinflammatory cytokines and may be useful for treating cytokine storm in patients with Covid-19 or other inflammatory lung diseases or trauma.

Early activation and recruitment of invariant natural killer T cells during liver ischemia-reperfusion: the major role of the alarmin interleukin-33

Over the past thirty years, the complexity of the αβ-T cell compartment has been enriched by the identification of innate-like T cells (ITCs), which are composed mainly of invariant natural killer T (iNKT) cells and mucosal-associated invariant T (MAIT) cells. Based on animal studies using ischemia-reperfusion (IR) models, a key role has been attributed to iNKT cells in close connection with the alarmin/cytokine interleukin (IL)-33, as early sensors of cell-stress in the initiation of acute sterile inflammation. Here we have investigated whether the new concept of a biological axis of circulating iNKT cells and IL-33 applies to humans, and may be extended to other ITC subsets, namely MAIT and γδ-T cells, in the acute sterile inflammation sequence occurring during liver transplant (LT). From a prospective biological collection of recipients, we reported that LT was accompanied by an early and preferential activation of iNKT cells, as attested by almost 40% of cells having acquired the expression of CD69 at the end of LT (i.e. 1-3 hours after portal reperfusion), as opposed to only 3-4% of conventional T cells. Early activation of iNKT cells was positively correlated with the systemic release of the alarmin IL-33 at graft reperfusion. Moreover, in a mouse model of hepatic IR, iNKT cells were activated in the periphery (spleen), and recruited in the liver in WT mice, as early as the first hour after reperfusion, whereas this phenomenon was virtually missing in IL-33-deficient mice. Although to a lesser degree than iNKT cells, MAIT and γδ-T cells also seemed targeted during LT, as attested by 30% and 10% of them acquiring CD69 expression, respectively. Like iNKT cells, and in clear contrast to γδ-T cells, activation of MAIT cells during LT was closely associated with both release of IL-33 immediately after graft reperfusion and severity of liver dysfunction occurring during the first three post-operative days. All in all, this study identifies iNKT and MAIT cells in connection with IL-33 as new key cellular factors and mechanisms of acute sterile inflammation in humans. Further investigations are required to confirm the implication of MAIT and iNKT cell subsets, and to precisely assess their functions, in the clinical course of sterile inflammation accompanying LT.

The adenosinergic machinery in cancer: In-tandem insights from basic mechanisms to therapy

Extracellular adenosine (eADO) signaling has emerged as an increasingly important regulator of immune responses, including tumor immunity. eADO is mainly produced from extracellular ATP (eATP) hydrolysis. eATP is rapidly accumulated in the extracellular space following cell death or cellular stress triggered by hypoxia, nutrient starvation, or inflammation. eATP plays a pro-inflammatory role by binding and activating the P2 purinergic receptors (P2X and P2Y), while eADO has been reported in many studies to mediate immunosuppression by activating the P1 purinergic receptors (A1, A2A, A2B, and A3) in diverse immune cells. Consequently, the hydrolysis of eATP to eADO alters the immunosurveillance in the tumor microenvironment (TME) not only by reducing eATP levels but also by enhancing adenosine receptor signaling. The effects of both P1 and P2 purinergic receptors are not restricted to immune cells. Here we review the most up-to-date understanding of the tumor adenosinergic system in all cell types, including immune cells, tumor cells, and stromal cells in TME. The potential novel directions of future adenosinergic therapies in immuno-oncology will be discussed.

Innate immunity and early liver inflammation

The innate system constitutes a first-line defence mechanism against pathogens. 80% of the blood supply entering the human liver arrives from the splanchnic circulation through the portal vein, so it is constantly exposed to immunologically active substances and pathogens from the gastrointestinal tract. Rapid neutralization of pathogens and toxins is an essential function of the liver, but so too is avoidance of harmful and unnecessary immune reactions. This delicate balance of reactivity and tolerance is orchestrated by a diverse repertoire of hepatic immune cells. In particular, the human liver is enriched in many innate immune cell subsets, including Kupffer cells (KCs), innate lymphoid cells (ILCs) like Natural Killer (NK) cells and ILC-like unconventional T cells - namely Natural Killer T cells (NKT), γδ T cells and Mucosal-associated Invariant T cells (MAIT). These cells reside in the liver in a memory-effector state, so they respond quickly to trigger appropriate responses. The contribution of aberrant innate immunity to inflammatory liver diseases is now being better understood. In particular, we are beginning to understand how specific innate immune subsets trigger chronic liver inflammation, which ultimately results in hepatic fibrosis. In this review, we consider the roles of specific innate immune cell subsets in early inflammation in human liver disease.

Innate Immune Cells during Machine Perfusion of Liver Grafts-The Janus Face of Hepatic Macrophages

Machine perfusion is an emerging technology in the field of liver transplantation. While machine perfusion has now been implemented in clinical routine throughout transplant centers around the world, a debate has arisen regarding its concurrent effect on the complex hepatic immune system during perfusion. Currently, our understanding of the perfusion-elicited processes involving innate immune cells remains incomplete. Hepatic macrophages (Kupffer cells) represent a special subset of hepatic immune cells with a dual pro-inflammatory, as well as a pro-resolving and anti-inflammatory, role in the sequence of ischemia-reperfusion injury. The purpose of this review is to provide an overview of the current data regarding the immunomodulatory role of machine perfusion and to emphasize the importance of macrophages for hepatic ischemia-reperfusion injury.

Gut Microbiota-Derived Unconventional T Cell Ligands: Contribution to Host Immune Modulation

Besides the prototypic innate and adaptive pathways, immune responses by innate-like lymphocytes have gained significant attention due to their unique roles. Among innate-like lymphocytes, unconventional T cells such as NKT cells and mucosal-associated invariant T (MAIT) cells recognize small nonpeptide molecules of specific chemical classes. Endogenous or microbial ligands are loaded to MHC class I-like molecule CD1d or MR1, and inducing immediate effector T cell and ligand structure is one of the key determinants of NKT/MAIT cell functions. Unconventional T cells are in close, constant contact with symbiotic microbes at the mucosal layer, and CD1d/MR1 can accommodate diverse metabolites produced by gut microbiota. There is a strong interest to identify novel immunoactive molecules of endobiotic (symbiont-produced) origin as new NKT/MAIT cell ligands, as well as new cognate Ags for previously uncharacterized unconventional T cell subsets. Further studies will open an possibility to explore basic biology as well as therapeutic potential.

Unconventional T cells and kidney disease

Unconventional T cells are a diverse and underappreciated group of relatively rare lymphocytes that are distinct from conventional CD4⁺ and CD8⁺ T cells, and that mainly recognize antigens in the absence of classical restriction through the major histocompatibility complex (MHC). These non-MHC-restricted T cells include mucosal-associated invariant T (MAIT) cells, natural killer T (NKT) cells, γδ T cells and other, often poorly defined, subsets. Depending on the physiological context, unconventional T cells may assume either protective or pathogenic roles in a range of inflammatory and autoimmune responses in the kidney. Accordingly, experimental models and clinical studies have revealed that certain unconventional T cells are potential therapeutic targets, as well as prognostic and diagnostic biomarkers. The responsiveness of human Vγ9Vδ2 T cells and MAIT cells to many microbial pathogens, for example, has implications for early diagnosis, risk stratification and targeted treatment of peritoneal dialysis-related peritonitis. The expansion of non-Vγ9Vδ2 γδ T cells during cytomegalovirus infection and their contribution to viral clearance suggest that these cells can be harnessed for immune monitoring and adoptive immunotherapy in kidney transplant recipients. In addition, populations of NKT, MAIT or γδ T cells are involved in the immunopathology of IgA nephropathy and in models of glomerulonephritis, ischaemia-reperfusion injury and kidney transplantation.

Irisin: A Promising Target for Ischemia-Reperfusion Injury Therapy

Ischemia-reperfusion injury (IRI) is defined as the total combined damage that occurs during a period of ischemia and following the recovery of blood flow. Oxidative stress, mitochondrial dysfunction, and an inflammatory response are factors contributing to IRI-related damage that can each result in cell death. Irisin is a polypeptide that is proteolytically cleaved from the extracellular domain of fibronectin type III domain-containing protein 5 (FNDC5). Irisin acts as a myokine that potentially mediates beneficial effects of exercise by reducing oxidative stress, improving mitochondrial fitness, and suppressing inflammation. The existing literature also suggests a possible link between irisin and IRI, involving mechanisms similar to those associated with exercise. This article will review the pathogenesis of IRI and the potential benefits and current limitations of irisin as a therapeutic strategy for IRI, while highlighting the mechanistic correlations between irisin and IRI.

Activation of iNKT Cells Facilitates Liver Repair After Hepatic Ischemia Reperfusion Injury Through Acceleration of Macrophage Polarization

Macrophage polarization is critical for liver tissue repair following acute liver injury. However, the underlying mechanisms of macrophage phenotype switching are not well defined. Invariant natural killer T (iNKT) cells orchestrate tissue inflammation and tissue repair by regulating cytokine production. Herein, we examined whether iNKT cells played an important role in liver repair after hepatic ischemia-reperfusion (I/R) injury by affecting macrophage polarization. To this end, we subjected male C57BL/6 mice to hepatic I/R injury, and mice received an intraperitoneal (ip) injection of α-galactosylceramide (α-GalCer) or vehicle. Compared with that of the vehicle, α-GalCer administration resulted in the promotion of liver repair accompanied by acceleration of macrophage differentiation and by increases in the numbers of Ly6C^high pro-inflammatory macrophages and Ly6C^low reparative macrophages. iNKT cells activated with α-GalCer produced interleukin (IL)-4 and interferon (IFN)-γ. Treatment with anti-IL-4 antibodies delayed liver repair, which was associated with an increased number of Ly6C^high macrophages and a decreased number of Ly6C^low macrophages. Treatment with anti-IFN-γ antibodies promoted liver repair, associated with reduced the number of Ly6C^high macrophages, but did not change the number of Ly6C^low macrophages. Bone marrow-derived macrophages up-regulated the expression of genes related to both a pro-inflammatory and a reparative phenotype when co-cultured with activated iNKT cells. Anti-IL-4 antibodies increased the levels of pro-inflammatory macrophage-related genes and decreased those of reparative macrophage-related genes in cultured macrophages, while anti-IFN-γ antibodies reversed the polarization of macrophages. Cd1d-deficient mice showed delayed liver repair and suppressed macrophage switching, compared with that in wild-type mice. These results suggest that the activation of iNKT cells by α-GalCer facilitated liver repair after hepatic I/R injury by both IL-4-and IFN-γ-mediated acceleration of macrophage polarization. Therefore, the activation of iNKT cells may represent a therapeutic tool for liver repair after hepatic I/R injury.

Targeting circadian PER2 as therapy in myocardial ischemia and reperfusion injury

The cycle of day and night dominates life on earth. Therefore, almost all living organisms adopted a molecular clock linked to the light-dark cycles. It is now well established that this molecular clock is crucial for human health and wellbeing. Disruption of the molecular clockwork directly results in a myriad of disorders, including cardiovascular diseases. Further, the onset of many cardiovascular diseases such as acute myocardial infarction exhibits a circadian periodicity with worse outcomes in the early morning hours. Based on these observations, the research community became interested in manipulating the molecular clock to treat cardiovascular diseases. In recent years, several exciting discoveries of pharmacological agents or molecular mechanisms targeting the molecular clockwork have paved the way for circadian medicine's arrival in cardiovascular diseases. The current review will outline the most recent circadian therapeutic advances related to the circadian rhythm protein Period2 (PER2) to treat myocardial ischemia and summarize future research in the respective field.

Influence of stereochemistry on the activity of rapadocin, an isoform-specific inhibitor of the nucleoside transporter ENT1

Rapadocin is a novel rapamycin-inspired polyketide–tetrapeptide hybrid macrocycle that possesses highly potent and isoform-specific inhibitory activity against the human equilibrative nucleoside transporter 1 (hENT1). Rapadocin contains an epimerizable chiral center in phenylglycine and an olefin group, and can thus exist as a mixture of four stereoisomers. Herein, we report the first total synthesis of the four stereoisomers of rapadocin using two different synthetic strategies and the assignment of their structures. The inhibitory activity of each of the four synthetic isomers on both hENT1 and hENT2 was determined. It was found that the stereochemistry of phenylglycine played a more dominant role than the configuration of the olefin in the activity of rapadocin. These findings will guide the future design and development of rapadocin analogs as new modulators of adenosine signaling.

Rapadocin is a novel rapamycin-inspired polyketide–tetrapeptide hybrid macrocycle that possesses highly potent and isoform-specific inhibitory activity against the human equilibrative nucleoside transporter 1 (hENT1).

Adenosine Signaling in the Tumor Microenvironment

Adenosine, deriving from ATP released by dying cancer cells and then degradated in the tumor environment by CD39/CD73 enzyme axis, is linked to the generation of an immunosuppressed niche favoring the onset of neoplasia. Signals delivered by extracellular adenosine are detected and transduced by G-protein-coupled cell surface receptors, classified into four subtypes: A₁, A_2A, A_2B, and A₃. A critical role of this nucleoside is emerging in the modulation of several immune and nonimmune cells defining the tumor microenvironment, providing novel insights about the development of novel therapeutic strategies aimed at undermining the immune-privileged sites where cancer cells grow and proliferate.

Purinergic signalling in liver diseases: Pathological functions and therapeutic opportunities

Extracellular nucleotides, including ATP, are essential regulators of liver function and serve as danger signals that trigger inflammation upon injury. Ectonucleotidases, which are expressed by liver-resident cells and recruited immune cells sequentially hydrolyse nucleotides to adenosine. The nucleotide/nucleoside balance orchestrates liver homeostasis, tissue repair, and functional restoration by regulating the crosstalk between liver-resident cells and recruited immune cells. In this review, we discuss our current knowledge on the role of purinergic signals in liver homeostasis, restriction of inflammation, stimulation of liver regeneration, modulation of fibrogenesis, and regulation of carcinogenesis. Moreover, we discuss potential targeted therapeutic strategies for liver diseases based on purinergic signals involving blockade of nucleotide receptors, enhancement of ectonucleoside triphosphate diphosphohydrolase activity, and activation of adenosine receptors.

Targeting of G-protein coupled receptors in sepsis

The Third International Consensus Definitions (Sepsis-3) define sepsis as life-threatening multi-organ dysfunction caused by a dysregulated host response to infection. Sepsis can progress to septic shock-an even more lethal condition associated with profound circulatory, cellular and metabolic abnormalities. Septic shock remains a leading cause of death in intensive care units and carries a mortality of almost 25%. Despite significant advances in our understanding of the pathobiology of sepsis, therapeutic interventions have not translated into tangible differences in the overall outcome for patients. Clinical trials of antagonists of various pro-inflammatory mediators in sepsis have been largely unsuccessful in the past. Given the diverse physiologic roles played by G-protein coupled receptors (GPCR), modulation of GPCR signaling for the treatment of sepsis has also been explored. Traditional pharmacologic approaches have mainly focused on ligands targeting the extracellular domains of GPCR. However, novel techniques aimed at modulating GPCR intracellularly through aptamers, pepducins and intrabodies have opened a fresh avenue of therapeutic possibilities. In this review, we summarize the diverse roles played by various subfamilies of GPCR in the pathogenesis of sepsis and identify potential targets for pharmacotherapy through these novel approaches.

N-Acetylcysteine Reduced Ischemia and Reperfusion Damage Associated with Steatohepatitis in Mice

N-acetylcysteine (NAC) is a pharmacological alternative with great potential for reducing the deleterious effects of surgical procedures on patients with steatohepatitis. We evaluated the effect of NAC on hepatic ischemia/reperfusion (I/R) injury in C57BL/6J mice, 8 weeks-old, weighing 25-30 g, with steatohepatitis induced by a methionine- and choline-deficient (MCD) diet. Groups: MCD group (steatohepatitis), MCD-I/R group (steatohepatitis plus 30 min of 70% liver ischemia and 24 h of reperfusion), MCD-I/R+NAC group (same as MCD-I/R group plus 150 mg/kg NAC 15 min before ischemia), and control group (normal AIN-93M diet). Liver enzymes and histopathology; nitrite and TBARS (thiobarbituric acid reactive substances) levels; pro-inflammatory cytokines; antioxidants enzymes; Nrf2 (nuclear factor erythroid-2-related factor 2) expression; and apoptosis were evaluated. In the group treated with NAC, reductions in inflammatory infiltration; AST (aspartate aminotransferase), nitrite, and TBARS levels; GPx (gutathione peroxidase) activity; cytokines synthesis; and number of apoptotic cells were observed while the GR (glutathione reductase) activity was increased. No differences were observed in Nfr2 expression or in SOD (superoxide dismutase), CAT (catalase), and GST (glutathione S-transferase) activities. Thus, it may be concluded that NAC exerts beneficial effects on mice livers with steatohepatitis submitted to I/R by reducing oxidative stress, inflammatory response, and cell death.

Pharmacological preconditioning with adenosine A1 receptor agonist induces immunosuppression and improves graft survival in novel allogeneic transplantation models

Adenosine is widely known as a potent modulator of innate and acquired immunity. It is released during transplants, and acts on four subtype receptors. In previous studies, we demonstrated that pharmacological preconditioning (PPC), pre-administration of the selective A1 receptor (A1R) agonist led to A1R desensitization, is followed by upregulation of the adenosine A2A receptor. This immunosuppressive effect resulted in lymphopenia, and it reduced T-cell reactivity. The aim of the current study was to challenge the immunosuppressive effects of A1R-PPC in models of allogeneic grafts. PPC mice were treated by intraperitoneal injection using specific adenosine A1R agonist 24 h and 12 h before starting any procedure. We challenged our method in novel allogeneic muscle and skin grafts models. Mice and grafts were assessed by complete blood counts, MLR from PPC splenocytes, and pathological evaluation. We found a significant reduction in WBC and lymphocyte counts in PPC-treated mice. Two-way MLR with splenocytes from PPC grafted mice showed decreased proliferation and anergy. Histology of PPC allogeneic grafts revealed profoundly less infiltration and even less muscle necrosis compared to vehicle treated allografts. Similar results observed in PPC skin transplantation. To conclude, PPC moderated graft rejection in separate allogeneic challenges, and reduced lymphocytes infiltration and ischemic damage.

Adenosine A2A receptor agonist (regadenoson) in human lung transplantation

BACKGROUND

Currently, there are no clinically approved treatments for ischemia-reperfusion injury after lung transplantation. Pre-clinical animal models have demonstrated a promising efficacy of adenosine _2A receptor (A_2AR) agonists as a treatment option for reducing ischemia-reperfusion injury. The purpose of this human study, is to conduct a Phase I clinical trial for evaluating the safety of continuous infusion of an A_2AR agonist in lung transplant recipients.

METHODS

An adaptive, two-stage continual reassessment trial was designed to evaluate the safety of regadenoson (A_2AR agonist) in the setting of lung transplantation. Continuous infusion of regadenoson was administered to lung transplant recipients that was started at the time of skin incision. Adverse events and dose-limiting toxicities, as pre-determined by a study team and assessed by a clinical team and an independent safety monitor, were the primary end-points for safety in this trial.

RESULTS

Between January 2018 and March 2019, 14 recipients were enrolled in the trial. Of these, 10 received the maximum infused dose of 1.44 µg/kg/min for 12 hours. No dose-limiting toxicities were observed. The steady-state plasma regadenoson levels sampled before the reperfusion of the first lung were 0.98 ± 0.46 ng/ml. There were no mortalities within 30 days.

CONCLUSIONS

Regadenoson, an A_2AR agonist, can be safely infused in the setting of lung transplantation with no dose-limiting toxicities or drug-related mortality. Although not powered for the evaluation of secondary end-points, the results of this trial and the outcome of pre-clinical studies warrant further investigation with a Phase II randomized controlled trial.

Innate immune cells, major protagonists of sickle cell disease pathophysiology

Sickle cell disease (SCD), considered the most common monogenic disease worldwide, is a severe hemoglobin disorder. Although the genetic and molecular bases have long been characterized, the pathophysiology remains incompletely elucidated and therapeutic options are limited. It has been increasingly suggested that innate immune cells, including monocytes, neutrophils, invariant natural killer T cells, platelets and mast cells, have a role in promoting inflammation, adhesion and pain in SCD. Here we provide a thorough review of the involvement of these novel, major protagonists in SCD pathophysiology, highlighting recent evidence for innovative therapeutic perspectives.

Exploring the complex role of chemokines and chemoattractants in vivo on leukocyte dynamics

Chemotaxis is fundamental for leukocyte migration in immunity and inflammation and contributes to the pathogenesis of many human diseases. Although chemokines and various other chemoattractants were initially appreciated as important mediators of acute inflammation, in the past years they have emerged as critical mediators of cell migration during immune surveillance, organ development, and cancer progression. Such advances in our knowledge in chemokine biology have paved the way for the development of specific pharmacological targets with great therapeutic potential. Chemoattractants may belong to different classes, including a complex chemokine system of approximately 50 endogenous molecules that bind to G protein-coupled receptors, which are expressed by a wide variety of cell types. Also, an unknown number of other chemoattractants may be generated by pathogens and damaged/dead cells. Therefore, blocking chemotaxis without causing side effects is an extremely challenging task. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the whole organ level in homeostasis, inflammation, and infection.

Metabolic Triggers of Invariant Natural Killer T-Cell Activation during Sterile Autoinflammatory Disease

Ample evidence exists for activation of invariant natural killer T (iNKT) cells in a sterile manner by endogenous ligands or microbial antigens from the commensal flora, indicating that iNKT cells are not truly self-tolerant. Their controlled autoreactivity state is disturbed in many types of sterile inflammatory disease, resulting in their central role in modulating autoimmune responses. This review focuses on sterile iNKT-cell responses that are initiated by metabolic triggers, such as obesity-associated inflammation and fatty liver disease, as a manifestation of metabolic disease and dyslipidemia, as well as ischemia reperfusion injuries and sickle cell disease, characterized by acute lack of oxygen and oxidative stress response on reperfusion. In the intestine, inflammation and iNKT-cell response type are shaped by the microbiome as an extended "self". Disease- and organ-specific differences in iNKT-cell response type are summarized and help to define common pathways that shape iNKT-cell responses in the absence of exogenous antigen.

Inhibition of the Adenosinergic Pathway in Cancer Rejuvenates Innate and Adaptive Immunity

The adenosine pathway plays a key role in modulating immune responses in physiological and pathological conditions. Physiologically, anti-inflammatory effects of adenosine balance pro-inflammatory adenosine 5'-triphosphate (ATP), protecting tissues from damage caused by activated immune cells. Pathologically, increased adenosine monophosphatase (AMPase) activity in tumors leads to increased adenosine production, generating a deeply immunosuppressed microenvironment and promoting cancer progression. Adenosine emerges as a promising target for cancer therapy. It mediates protumor activities by inducing tumor cell proliferation, angiogenesis, chemoresistance, and migration/invasion by tumor cells. It also inhibits the functions of immune cells, promoting the formation of a tumor-permissive immune microenvironment and favoriting tumor escape from the host immune system. Pharmacologic inhibitors, siRNA or antibodies specific for the components of the adenosine pathway, or antagonists of adenosine receptors have shown efficacy in pre-clinical studies in various in vitro and in vivo tumor models and are entering the clinical arena. Inhibition of the adenosine pathway alone or in combination with classic immunotherapies offers a potentially effective therapeutic strategy in cancer.

Protective Role of mTOR in Liver Ischemia/Reperfusion Injury: Involvement of Inflammation and Autophagy

Liver ischemia/reperfusion (IR) injury is a common phenomenon after liver resection and transplantation, which often results in liver graft dysfunction such as delayed graft function and primary nonfunction. The mammalian target of rapamycin (mTOR) is an evolutionarily highly conserved serine/threonine protein kinase, which coordinates cell growth and metabolism through sensing environmental inputs under physiological or pathological conditions, involved in the pathophysiological process of IR injury. In this review, we mainly present current evidence of the beneficial role of mTOR in modulating inflammation and autophagy under liver IR to provide some evidence for the potential therapies for liver IR injury.

Cell type- and tissue-specific functions of ecto-5'-nucleotidase (CD73)

Ecto-5'-nucleotidase [cluster of differentiation 73 (CD73)] is a ubiquitously expressed glycosylphosphatidylinositol-anchored glycoprotein that converts extracellular adenosine 5'-monophosphate to adenosine. Anti-CD73 inhibitory antibodies are currently undergoing clinical testing for cancer immunotherapy. However, many protective physiological functions of CD73 need to be taken into account for new targeted therapies. This review examines CD73 functions in multiple organ systems and cell types, with a particular focus on novel findings from the last 5 years. Missense loss-of-function mutations in the CD73-encoding gene NT5E cause the rare disease "arterial calcifications due to deficiency of CD73." Aside from direct human disease involvement, cellular and animal model studies have revealed key functions of CD73 in tissue homeostasis and pathology across multiple organ systems. In the context of the central nervous system, CD73 is antinociceptive and protects against inflammatory damage, while also contributing to age-dependent decline in cortical plasticity. CD73 preserves barrier function in multiple tissues, a role that is most evident in the respiratory system, where it inhibits endothelial permeability in an adenosine-dependent manner. CD73 has important cardioprotective functions during myocardial infarction and heart failure. Under ischemia-reperfusion injury conditions, rapid and sustained induction of CD73 confers protection in the liver and kidney. In some cases, the mechanism by which CD73 mediates tissue injury is less clear. For example, CD73 has a promoting role in liver fibrosis but is protective in lung fibrosis. Future studies that integrate CD73 regulation and function at the cellular level with physiological responses will improve its utility as a disease target.

Tissue-specific functions of invariant natural killer T cells

Invariant natural killer T cells (iNKT cells) are an innate-like T cell subset that expresses an invariant T cell receptor (TCR) α-chain and recognizes lipids presented on CD1d. They secrete diverse cytokines and can influence many types of immune responses. Despite having highly similar TCR specificities, iNKT cells differentiate in the thymus into distinct subsets that are analogous to T helper 1 (T_H1), T_H2 and T_H17 cell subsets. Additional iNKT cell subsets that may require peripheral activation have also been described, including one that produces IL-10. In general, iNKT cells are non-circulating, tissue-resident lymphocytes, but the prevalence of different iNKT cell subsets differs markedly between tissues. Here, we summarize the functions of iNKT cells in four tissues in which they are prevalent, namely, the liver, the lungs, adipose tissue and the intestine. Importantly, we explain how local iNKT cell responses at each site contribute to tissue homeostasis and protection from infection but can also contribute to tissue inflammation and damage.

Hypoxia signaling in human diseases and therapeutic targets

Since the discovery of hypoxia-inducible factor (HIF), numerous studies on the hypoxia signaling pathway have been performed. The role of HIF stabilization during hypoxia has been extended from the induction of a single gene erythropoietin to the upregulation of a couple of hundred downstream targets, which demonstrates the complexity and importance of the HIF signaling pathway. Accordingly, HIF and its downstream targets are emerging as novel therapeutic options to treat various organ injuries. In this review, we discuss the current understanding of HIF signaling in four different organ systems, including the heart, lung, liver, and kidney. We also discuss the divergent roles of HIF in acute and chronic disease conditions and their revealed functions. Finally, we introduce some of the efforts that are being performed to translate our current knowledge in hypoxia signaling to clinical medicine.

Protective role of heme oxygenase-1 in fatty liver ischemia-reperfusion injury

Ischemia-reperfusion (IR) injury is a kind of injury resulting from the restoration of the blood supply after blood vessel closure during liver transplantation and is the main cause of graft failure. The pathophysiological mechanisms of hepatic IR include a variety of oxidative stress responses. Hepatic IR is characterized by ischemia and hypoxia inducing oxidative stress, immune response and apoptosis. Fat-denatured livers are also used as donors due to the lack of liver donors. Fatty liver is less tolerant to IR than normal liver. Heme oxygenase (HO) is an enzyme that breaks down hemoglobin to bilirubin, ferrous iron and carbon monoxide (CO). Inducible HO subtype HO-1 is an important protective molecule in mammalian cells used to improve acute and chronic liver injury owing to its characteristic anti-inflammatory and anti-apoptotic qualities. HO-1 degrades heme, and its reaction product CO has been shown to reduce hepatic IR injury and increase the survival rate of grafts. As an induced form of HO, HO-1 also exerts a protective effect against liver IR injury and may be useful as a new strategy of ameliorating this kind of damage. This review summarizes the protective effects of HO-1 in liver IR injury, especially in fatty liver.

CXCR6 deficiency ameliorates ischemia-reperfusion injury by reducing the recruitment and cytokine production of hepatic NKT cells in a mouse model of non-alcoholic fatty liver disease

Fatty liver is used for transplantation due to organ shortage, but prone to cause complications like ischemia-reperfusion injury (IRI). NKT cells as a bridge between innate and adaptive immunity were reported to infiltrate the liver at the early phase of IRI induced in normal liver. However, the localization mechanism of NKT cells is not precise, and the role of NKT cells in fatty liver IRI is poorly understood. In present murine IRI model of non-alcoholic fatty liver disease, we demonstrated that although the number reduced in fatty liver, NKT cells still activated and accumulated to fatty liver following IRI, and contributed to IRI by producing inflammatory cytokine IFN-γ. We revealed that NKT cells in fatty liver expressed more CXCR6, a vital chemokine receptor; meanwhile, the ligand CXCL16 mRNA expression level in fatty liver was up-regulated. The up-regulation of the CXCR6/CXCL16 axis in fatty liver happened in IRI, which maybe endow NKT cells more chemotaxis. We further found CXCR6 deficiency reduced the recruitment of NKT cells in a tissue-dependent manner, and impaired the IFN-γ producing capacity of hepatic NKT cells. Serum ALT level and hepatic histology were both improved in CXCR6 deficient mice. The results provide evidence of the pathogenic role of NKT cells in fatty liver IRI, and important localization mechanism involving up-regulated CXCR6/CXCL16. Deficiency of CXCR6 protects the fatty liver from IRI by reducing the recruitment and cytokine production of hepatic NKT cells.

Purine Release, Metabolism, and Signaling in the Inflammatory Response

ATP, NAD⁺, and nucleic acids are abundant purines that, in addition to having critical intracellular functions, have evolved extracellular roles as danger signals released in response to cell lysis, apoptosis, degranulation, or membrane pore formation. In general ATP and NAD⁺ have excitatory and adenosine has anti-inflammatory effects on immune cells. This review focuses on recent advances in our understanding of purine release mechanisms, ectoenzymes that metabolize purines (CD38, CD39, CD73, ENPP1, and ENPP2/autotaxin), and signaling by key P2 purinergic receptors (P2X7, P2Y2, and P2Y12). In addition to metabolizing ATP or NAD⁺, some purinergic ectoenzymes metabolize other inflammatory modulators, notably lysophosphatidic acid and cyclic GMP-AMP (cGAMP). Also discussed are extracellular signaling effects of NAD⁺ mediated by ADP-ribosylation, and epigenetic effects of intracellular adenosine mediated by modification of S-adenosylmethionine-dependent DNA methylation.

Innate T cells in the intensive care unit

Rapid onset of acute inflammation is a hallmark of critical illnesses that bring patients to the intensive care unit (ICU). In critical illness, innate T cells rapidly reach full activation and drive a robust acute inflammatory response. As "cellular adjuvants," innate T cells worsen inflammation and mortality in several common critical illnesses including sepsis, ischemia-reperfusion injury, stroke, and exacerbations of respiratory disease. Interestingly, innate T cell subsets can also promote a protective and anti-inflammatory response in sepsis, ischemia-reperfusion injury, and asthma. Therapies that target innate T cells have been validated in several models of critical illness. Here, we review the role of natural killer T (NKT) cells, mucosal-associated invariant T (MAIT) cells and γδ T cells in clinical and experimental critical illness.

Rapamycin-inspired macrocycles with new target specificity

Rapamycin and FK506 are macrocyclic natural products with an extraordinary mode of action—they form binary complexes with FKBP through a shared FKBP-binding domain before forming ternary complexes with their respective targets, mTOR and calcineurin, respectively. Inspired by this, we sought to build a rapamycin-like macromolecule library to target new cellular proteins by replacing the effector domain of rapamycin with a combinatorial library of oligopeptides. We developed a robust macrocyclization method using ring-closing metathesis and synthesized a 45,000-compound library of hybrid macrocycles that are named rapafucins using optimized FKBP-binding domains. Screening of the rapafucin library in human cells led to the discovery of rapadocin, an inhibitor of nucleoside uptake. Rapadocin is a potent, isoform-specific and FKBP-dependent inhibitor of the equilibrative nucleoside transporter 1 and is efficacious in an animal model of kidney ischemia reperfusion injury. Together, these results demonstrate that rapafucins are a new class of chemical probes and drug leads that can expand the repertoire of protein targets well beyond mTOR and calcineurin.

Targeting Adenosine Receptor Signaling in Cancer Immunotherapy

The immune system plays a major role in the surveillance and control of malignant cells, with the presence of tumor infiltrating lymphocytes (TILs) correlating with better patient prognosis in multiple tumor types. The development of ‘checkpoint blockade’ and adoptive cellular therapy has revolutionized the landscape of cancer treatment and highlights the potential of utilizing the patient’s own immune system to eradicate cancer. One mechanism of tumor-mediated immunosuppression that has gained attention as a potential therapeutic target is the purinergic signaling axis, whereby the production of the purine nucleoside adenosine in the tumor microenvironment can potently suppress T and NK cell function. The production of extracellular adenosine is mediated by the cell surface ectoenzymes CD73, CD39, and CD38 and therapeutic agents have been developed to target these as well as the downstream adenosine receptors (A₁R, A_2AR, A_2BR, A₃R) to enhance anti-tumor immune responses. This review will discuss the role of adenosine and adenosine receptor signaling in tumor and immune cells with a focus on their cell-specific function and their potential as targets in cancer immunotherapy.

Activation of natural killer T cells contributes to triptolide-induced liver injury in mice

Triptolide (TP) is the main active ingredient of Tripterygium wilfordii Hook.f, which has attracted great interest due to its promising efficacy for autoimmune diseases and tumors. However, severe adverse reactions, especially hepatotoxicity, have restricted its approval in the market. In the present study we explored the role of hepatic natural killer T (NKT) cells in the pathogenesis of TP-induced liver injury in mice. TP (600 μg/kg/day, i.g.) was administered to female mice for 1, 3, or 5 days. We found that administration of TP dose-dependently induced hepatotoxicity, evidenced by the body weight reduction, elevated serum ALT and AST levels, as well as significant histopathological changes in the livers. However, the mice were resistant to the development of TP-induced liver injury when their NKT cells were depleted by injection of anti-NK1.1 mAb (200 μg, i.p.) on days -2 and -1 before TP administration. We further revealed that TP administration activated NKT cells, dominantly releasing Th1 cytokine IFN-γ, recruiting neutrophils and macrophages, and leading to liver damage. After anti-NK1.1 injection, however, the mice mainly secreted Th2 cytokine IL-4 in the livers and exhibited a significantly lower percentage of hepatic infiltrating neutrophils and macrophages upon TP challenge. The activation of NKT cells was associated with the upregulation of Toll-like receptor (TLR) signaling pathway. Collectively, these results demonstrate a novel role of NKT cells contributing to the mechanisms of TP-induced liver injury. More importantly, the regulation of NKT cells may promote effective measures that control drug-induced liver injury.

The Impact of Invariant NKT Cells in Sterile Inflammation: The Possible Contribution of the Alarmin/Cytokine IL-33

Although the contribution of iNKT cells to induction of sterile inflammation is now well-established, the nature of the endogenous compounds released early after cellular stress or damage that drive their activation and recruitment remains poorly understood. More precisely, iNKT cells have not been described as being reactive to endogenous non-protein damage-associated molecular-pattern molecules (DAMPs). A second subset of DAMPs, called alarmins, are tissue-derived nuclear proteins, constitutively expressed at high levels in epithelial barrier tissues and endothelial barriers. These potent immunostimulants, immediately released after tissue damage, include the alarmin IL-33. This factor has aroused interest due to its singular action as an alarmin during infectious, allergic responses and acute tissue injury, and as a cytokine, contributing to the latter resolutive/repair phase of sterile inflammation. IL-33 targets iNKT cells, inducing their recruitment in an inflammatory state, and amplifying their regulatory and effector functions. In the present review, we introduce the new concept of a biological axis of iNKT cells and IL-33, involved in alerting and controlling the immune cells in experimental models of sterile inflammation. This review will focus on acute organ injury models, especially ischemia-reperfusion injury, in the kidneys, liver and lungs, where iNKT cells and IL-33 have been presumed to mediate and/or control the injury mechanisms, and their potential relevance in human pathophysiology.

Induction of antiinflammatory purinergic signaling in activated human iNKT cells

Invariant natural killer T (iNKT) cells are activated at sites of local tissue injury, or globally during vaso-occlusive episodes of sickle cell disease (SCD). Tissue damage stimulates production of CD1d-restricted lipid antigens that activate iNKT cells to produce Th1- and Th2-type cytokines. Here, we show that circulating iNKT cells in SCD patients express elevated levels of the ectonucleoside triphosphate diphosphosphohydrolase, CD39, as well the adenosine A2A receptor (A2AR). We also investigated the effects of stimulating cultured human iNKT cells on the expression of genes involved in the regulation of purinergic signaling. iNKT cell stimulation caused induction of ADORA2A, P2RX7, CD38, CD39, ENPP1, CD73, PANX1, and ENT1. Transcription of ADA, which degrades adenosine, was reduced. Induction of CD39 mRNA was associated with increased ecto-ATPase activity on iNKT cells that was blocked by POM1. Exposure of iNKT cells to A2AR agonists during stimulation reduced production of IFN-γ and enhanced production of IL-13 and CD39. Based on these findings, we define "purinergic Th2-type cytokine bias" as an antiinflammatory purinergic response to iNKT cell stimulation resulting from changes in the transcription of several genes involved in purine release, extracellular metabolism, and signaling.

Epithelial and Endothelial Pannexin1 Channels Mediate AKI

Background Pannexin1 (Panx1), an ATP release channel, is present in most mammalian tissues, but the role of Panx1 in health and disease is not fully understood. Panx1 may serve to modulate AKI; ATP is a precursor to adenosine and may function to block inflammation, or ATP may act as a danger-associated molecular pattern and initiate inflammation.Methods We used pharmacologic and genetic approaches to evaluate the effect of Panx1 on kidney ischemia-reperfusion injury (IRI), a mouse model of AKI.Results Pharmacologic inhibition of gap junctions, including Panx1, by administration of carbenoxolone protected mice from IRI. Furthermore, global deletion of Panx1 preserved kidney function and morphology and diminished the expression of proinflammatory molecules after IRI. Analysis of bone marrow chimeric mice revealed that Panx1 expressed on parenchymal cells is necessary for ischemic injury, and both proximal tubule and vascular endothelial Panx1 tissue-specific knockout mice were protected from IRI. In vitro, Panx1-deficient proximal tubule cells released less and retained more ATP under hypoxic stress.Conclusions Panx1 is involved in regulating ATP release from hypoxic cells, and reducing this ATP release may protect kidneys from AKI.