Adenosine A2A receptor activation inhibits T helper 1 and T helper 2 cell development and effector function

Insight into adenosine pathway in psoriasis: Elucidating its role and the potential therapeutical applications

Psoriasis is an inflammatory skin disease, that can manifest as different phenotypes, however its most common form is psoriasis vulgaris (plaque psoriasis), characterized by abnormal keratinocyte proliferation, leading to characteristic histopathological signs of acanthosis, hyperkeratosis and parakeratosis. For many years, there has been a debate regarding whether keratinocyte dysfunction leads to immune system dysregulation in psoriasis or vice versa. It is now understood that epidermal hyperplasia results from immune system activation. Besides epidermal hyperplasia, psoriatic skin shows leukocyte infiltration, evident angiogenesis in the papillary dermis, characterized by tortuous, dilated capillaries, as well as oedema. There is substantial early evidence that adenosine is a key mediator of the immune response; it derives from ATP hydrolysis and accumulates into tissue in response to systemic and local stress conditions, hypoxia, metabolic stress, inflammation. Adenosine controls several cell functions by signalling through its 4 receptor subtypes, A1, A2A, A2B and A3. Evidence suggests that adenosine may play a role in psoriasis pathogenesis by controlling several immune cell functions, keratinocyte proliferation, neo-angiogenesis. Expression of adenosine receptor varies in psoriatic skin, and this can significantly impact on tissue homeostasis. Indeed, an altered adenosine receptor profile may contribute to the dysregulation observed in psoriasis, affecting immune responses and inflammatory pathways. Here, we discuss the role of adenosine in regulating the functions of the main cell populations implied in the pathogenesis of psoriasis. Furthermore, we give evidence for adenosine signalling pathway as target for therapeutic intervention in psoriasis.

The reduced frequency of CD39+CD73+ B cell subsets in SLE patients is correlated with disease activity

BACKGROUND

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease characterized by immune mechanisms dysregulation, leading to the production of diverse autoantibodies. However, the immune pathways underlying B-cell function and phenotypic abnormalities related to SLE pathogenesis remain incompletely understood.

OBJECTIVE

To explore new markers of SLE activity and potential targets for SLE immunotherapy.

METHODS

Collect peripheral blood mononuclear cells (PBMCs) from SLE patients and healthy controls (HC). Use flow cytometry to detect CD39 and CD73 expression on B cell subsets and enzyme-linked immunosorbent assay (ELISA) to measure adenosine (ADO) concentrations in SLE patients' serum. Compare CD39+CD73+ B cell subsets frequency and ADO concentrations in SLE patients and HC group. Additionally, analyze the correlation between CD39+CD73+ B cell subsets frequency and clinical laboratory parameters.

RESULTS

CD39 and CD73 are simultaneously highly expressed on CD19+ B cell subsets, with significantly lower frequency of CD39+CD73+ B cell subsets in SLE patients compared to HC group. This frequency negatively correlates with Systemic Lupus Erythematosus Disease Activity Index (SLEDAI), C-reactive protein (CRP), and anti-double-stranded DNA (anti-dsDNA) antibodies, while positively correlating with IgM and prothrombin time (PT). Additionally, the frequency of CD39+CD73+ B cell subsets is significantly negatively correlated with IL-6 and IFN-α. In vitro cell experiments demonstrate that adenosine significantly inhibits R848-induced inflammatory cytokine production in a dose-dependent manner.

CONCLUSION

The frequency of CD39+CD73+ B cell subsets of SLE patients is decreased, correlating with clinical laboratory parameters and disease activity. Simultaneously, ADO concentration in the patients' serum is reduced. The CD39+CD73+ B cell/ADO pathway may represent a novel immunotherapy strategy for SLE.

Mesenchymal Stem/Stromal Cells Derived from Dental Tissues Mediate the Immunoregulation of T Cells through the Purinergic Pathway

Human dental tissue mesenchymal stem cells (DT-MSCs) constitute an attractive alternative to bone marrow-derived mesenchymal stem cells (BM-MSCs) for potential clinical applications because of their accessibility and anti-inflammatory capacity. We previously demonstrated that DT-MSCs from dental pulp (DP-MSCs), periodontal ligaments (PDL-MSCs), and gingival tissue (G-MSCs) show immunosuppressive effects similar to those of BM, but to date, the DT-MSC-mediated immunoregulation of T lymphocytes through the purinergic pathway remains unknown. In the present study, we compared DP-MSCs, PDL-MSCs, and G-MSCs in terms of CD26, CD39, and CD73 expression; their ability to generate adenosine (ADO) from ATP and AMP; and whether the concentrations of ADO that they generate induce an immunomodulatory effect on T lymphocytes. BM-MSCs were included as the gold standard. Our results show that DT-MSCs present similar characteristics among the different sources analyzed in terms of the properties evaluated; however, interestingly, they express more CD39 than BM-MSCs; therefore, they generate more ADO from ATP. In contrast to those produced by BM-MSCs, the concentrations of ADO produced by DT-MSCs from ATP inhibited the proliferation of CD3+ T cells and promoted the generation of CD4+CD25+FoxP3+CD39+CD73+ Tregs and Th17+CD39+ lymphocytes. Our data suggest that DT-MSCs utilize the adenosinergic pathway as an immunomodulatory mechanism and that this mechanism is more efficient than that of BM-MSCs.

Adenosine and Its Receptors in the Pathogenesis and Treatment of Inflammatory Skin Diseases

Inflammatory skin diseases highlight inflammation as a central driver of skin pathologies, involving a multiplicity of mediators and cell types, including immune and non-immune cells. Adenosine, a ubiquitous endogenous immune modulator, generated from adenosine triphosphate (ATP), acts via four G protein-coupled receptors (A1, A2A, A2B, and A3). Given the widespread expression of those receptors and their regulatory effects on multiple immune signaling pathways, targeting adenosine receptors emerges as a compelling strategy for anti-inflammatory intervention. Animal models of psoriasis, contact hypersensitivity (CHS), and other dermatitis have elucidated the involvement of adenosine receptors in the pathogenesis of these conditions. Targeting adenosine receptors is effective in attenuating inflammation and remodeling the epidermal structure, potentially showing synergistic effects with fewer adverse effects when combined with conventional therapies. What is noteworthy are the promising outcomes observed with A2A agonists in animal models and ongoing clinical trials investigating A3 agonists, underscoring a potential therapeutic approach for the management of inflammatory skin disorders.

Critical role of the gut microbiota in immune responses and cancer immunotherapy

The gut microbiota plays a critical role in the progression of human diseases, especially cancer. In recent decades, there has been accumulating evidence of the connections between the gut microbiota and cancer immunotherapy. Therefore, understanding the functional role of the gut microbiota in regulating immune responses to cancer immunotherapy is crucial for developing precision medicine. In this review, we extract insights from state-of-the-art research to decipher the complicated crosstalk among the gut microbiota, the systemic immune system, and immunotherapy in the context of cancer. Additionally, as the gut microbiota can account for immune-related adverse events, we discuss potential interventions to minimize these adverse effects and discuss the clinical application of five microbiota-targeted strategies that precisely increase the efficacy of cancer immunotherapy. Finally, as the gut microbiota holds promising potential as a target for precision cancer immunotherapeutics, we summarize current challenges and provide a general outlook on future directions in this field.

Immune cell expression patterns of CD39/CD73 ectonucleotidases in rodent models of cardiac arrest and resuscitation

Background

Cardiac arrest (CA) is a significant public health concern. There is the high imminent mortality and survival in those who are resuscitated is substantively compromised by the post-CA syndrome (PCAS), characterized by multiorgan ischemia-reperfusion injury (IRI). The inflammatory response in PCAS is complex and involves various immune cell types, including lymphocytes and myeloid cells that have been shown to exacerbate organ IRI, such as myocardial infarction. Purinergic signaling, as regulated by CD39 and CD73, has emerged as centrally important in the context of organ-specific IRI. Hence, comprehensive understanding of such purinergic responses may be likewise imperative for improving outcomes in PCAS.

Methods

We have investigated alterations of immune cell populations after CA by utilizing rodent models of PCAS. Blood and spleen were collected after CA and resuscitation and underwent flow cytometry analysis to evaluate shifts in CD3+CD4+ helper T cells, CD3+CD8a+ cytotoxic T cells, and CD4/CD8a ratios. We then examined the expression of CD39 and CD73 across diverse cell types, including myeloid cells, T lymphocytes, and B lymphocytes.

Results

In both rat and mouse models, there were significant increases in the frequency of CD3+CD4+ T lymphocytes in PCAS (rat, P < 0.01; mouse, P < 0.001), with consequently elevated CD4/CD8a ratios in whole blood (both, P < 0.001). Moreover, CD39 and CD73 expression on blood leukocytes were markedly increased (rat, P < 0.05; mouse, P < 0.01 at 24h). Further analysis in the experimental mouse model revealed that CD11b+ myeloid cells, with significant increase in their population (P < 0.01), had high level of CD39 (88.80 ± 2.05 %) and increased expression of CD73 (P < 0.05). CD19+ B lymphocytes showed slight increases of CD39 (P < 0.05 at 2h) and CD73 (P < 0.05 at 2h), while, CD3+ T lymphocytes had decreased levels of them. These findings suggested a distinct patterns of expression of CD39 and CD73 in these specific immune cell populations after CA.

Conclusions

These data have provided comprehensive insights into the immune response after CA, highlighting high-level expressions of CD39 and CD73 in myeloid cells.

Low Density Lipoprotein Cholesterol Decreases the Expression of Adenosine A2A Receptor and Lipid Rafts-Protein Flotillin-1: Insights on Cardiovascular Risk of Hypercholesterolemia

High blood levels of low-density lipoprotein (LDL)-cholesterol (LDL-C) are associated with atherosclerosis, mainly by promoting foam cell accumulation in vessels. As cholesterol is an essential component of cell plasma membranes and a regulator of several signaling pathways, LDL-C excess may have wider cardiovascular toxicity. We examined, in untreated hypercholesterolemia (HC) patients, selected regardless of the cause of LDL-C accumulation, and in healthy participants (HP), the expression of the adenosine A2A receptor (A2AR), an anti-inflammatory and vasodilatory protein with cholesterol-dependent modulation, and Flotillin-1, protein marker of cholesterol-enriched plasma membrane domains. Blood cardiovascular risk and inflammatory biomarkers were measured. A2AR and Flotillin-1 expression in peripheral blood mononuclear cells (PBMC) was lower in patients compared to HP and negatively correlated to LDL-C blood levels. No other differences were observed between the two groups apart from transferrin and ferritin concentrations. A2AR and Flotillin-1 proteins levels were positively correlated in the whole study population. Incubation of HP PBMCs with LDL-C caused a similar reduction in A2AR and Flotillin-1 expression. We suggest that LDL-C affects A2AR expression by impacting cholesterol-enriched membrane microdomains. Our results provide new insights into the molecular mechanisms underlying cholesterol toxicity, and may have important clinical implication for assessment and treatment of cardiovascular risk in HC.

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.

Purinergic system in cancer stem cells

Accumulating evidence supports the idea that cancer stem cells (CSCs) are those with the capacity to initiate tumors, generate phenotypical diversity, sustain growth, confer drug resistance, and orchestrate the spread of tumor cells. It is still controversial whether CSCs originate from normal stem cells residing in the tissue or cancer cells from the tumor bulk that have dedifferentiated to acquire stem-like characteristics. Although CSCs have been pointed out as key drivers in cancer, knowledge regarding their physiology is still blurry; thus, research focusing on CSCs is essential to designing novel and more effective therapeutics. The purinergic system has emerged as an important autocrine-paracrine messenger system with a prominent role at multiple levels of the tumor microenvironment, where it regulates cellular aspects of the tumors themselves and the stromal and immune systems. Recent findings have shown that purinergic signaling also participates in regulating the CSC phenotype. Here, we discuss updated information regarding CSCs in the purinergic system and present evidence supporting the idea that elements of the purinergic system expressed by this subpopulation of the tumor represent attractive pharmacological targets for proposing innovative anti-cancer therapies.

Adenosine in cancer immunotherapy: Taking off on a new plane

As a new pillar of cancer therapy, tumor immunotherapy has brought irreplaceable durable responses in tumors. Considering its low response rate, additional immune regulatory mechanisms will be critical for the development of next-generation immune therapeutics. As a key regulatory mechanism, adenosine (ADO) protects tissues from excessive immune responses, but as a metabolite highly concentrated in tumor microenvironments, extracellular adenosine acts on adenosine receptors (mainly A2A receptors) expressed on MDSCs, Tregs, NK cells, effector T cells, DCs, and macrophages to promote tumor cell escape from immune surveillance by inhibiting the immune response. Amounting preclinical studies have demonstrated the adenosine pathway as a novel checkpoint for immunotherapy. Large number of adenosine pathway targeting clinical trials are now underway, including antibodies against CD39 and CD73 as well as A2A receptor inhibitors. There has been evidence of antitumor efficacy of these inhibitors in early clinical trials among a variety of tumors such as breast cancer, prostate cancer, non-small cell lung cancer, etc. As more clinical trial results are published, the combination of blockade of this pathway with immune checkpoint inhibitors, targeted drugs, traditional chemotherapy medications, radiotherapy and endocrine therapy will provide cancer patients with better clinical outcomes. We would elaborate on the role of CD39-CD73-A2AR pathway in the contribution of tumor microenvironment and the targeting of the adenosinergic pathway for cancer therapy in the review.

Adenosine, bridging chronic inflammation and tumor growth

Adenosine (Ado) is a well-known immunosuppressive agent that may be released or generated extracellularly by cells, via degrading ATP by the sequential actions of the ectonucleotides CD39 and CD73. During inflammation Ado is produced by leukocytes and tissue cells by different means to initiate the healing phase. Ado downregulates the activation and the effector functions of different leukocyte (sub-) populations and stimulates proliferation of fibroblasts for re-establishment of intact tissues. Therefore, the anti-inflammatory actions of Ado are already intrinsically triggered during each episode of inflammation. These tissue-regenerating and inflammation-tempering purposes of Ado can become counterproductive. In chronic inflammation, it is possible that Ado-driven anti-inflammatory actions sustain the inflammation and prevent the final clearance of the tissues from possible pathogens. These chronic infections are characterized by increased tissue damage, remodeling and accumulating DNA damage, and are thus prone for tumor formation. Developing tumors may further enhance immunosuppressive actions by producing Ado by themselves, or by "hijacking" CD39+/CD73+ cells that had already developed during chronic inflammation. This review describes different and mostly convergent mechanisms of how Ado-induced immune suppression, initially induced in inflammation, can lead to tumor formation and outgrowth.

Gut microbiota: key facilitator in metastasis of colorectal cancer

Colorectal cancer (CRC) ranks third in terms of incidence among all kinds of cancer. The main cause of death is metastasis. Recent studies have shown that the gut microbiota could facilitate cancer metastasis by promoting cancer cells proliferation, invasion, dissemination, and survival. Multiple mechanisms have been implicated, such as RNA-mediated targeting effects, activation of tumor signaling cascades, secretion of microbiota-derived functional substances, regulation of mRNA methylation, facilitated immune evasion, increased intravasation of cancer cells, and remodeling of tumor microenvironment (TME). The understanding of CRC metastasis was further deepened by the mechanisms mentioned above. In this review, the mechanisms by which the gut microbiota participates in the process of CRC metastasis were reviewed as followed based on recent studies.

The Clinical Significance of CD73 in Cancer

The search for new and effective treatment targets for cancer immunotherapy is an ongoing challenge. Alongside the more established inhibitory immune checkpoints, a novel potential target is CD73. As one of the key enzymes in the purinergic signalling pathway CD73 is responsible for the generation of immune suppressive adenosine. The expression of CD73 is higher in tumours than in the corresponding healthy tissues and associated with a poor prognosis. CD73, mainly by the production of adenosine, is critical in the suppression of an adequate anti-tumour immune response, but also in promoting cancer cell proliferation, tumour growth, angiogenesis, and metastasis. The upregulation of CD73 and generation of adenosine by tumour or tumour-associated immune cells is a common resistance mechanism to many cancer treatments such as chemotherapy, radiotherapy, targeted therapy, and immunotherapy. Therefore, the inhibition of CD73 represents a new and promising approach to increase therapy efficacy. Several CD73 inhibitors have already been developed and successfully demonstrated anti-cancer activity in preclinical studies. Currently, clinical studies evaluate CD73 inhibitors in different therapy combinations and tumour entities. The initial results suggest that inhibiting CD73 could be an effective option to augment anti-cancer immunotherapeutic strategies. This review provides an overview of the rationale behind the CD73 inhibition in different treatment combinations and the role of CD73 as a prognostic marker.

Adenosine metabolized from extracellular ATP ameliorates organ injury by triggering A2BR signaling

BACKGROUND

Trauma and a subsequent hemorrhagic shock (T/HS) result in insufficient oxygen delivery to tissues and multiple organ failure. Extracellular adenosine, which is a product of the extracellular degradation of adenosine 5' triphosphate (ATP) by the membrane-embedded enzymes CD39 and CD73, is organ protective, as it participates in signaling pathways, which promote cell survival and suppress inflammation through adenosine receptors including the A2BR. The aim of this study was to evaluate the role of CD39 and CD73 delivering adenosine to A2BRs in regulating the host's response to T/HS.

METHODS

T/HS shock was induced by blood withdrawal from the femoral artery in wild-type, global knockout (CD39, CD73, A2BR) and conditional knockout (intestinal epithelial cell-specific deficient VillinCre-A2BRfl/fl) mice. At 3 three hours after resuscitation, blood and tissue samples were collected to analyze organ injury.

RESULTS

T/HS upregulated the expression of CD39, CD73, and the A2BR in organs. ATP and adenosine levels increased after T/HS in bronchoalveolar lavage fluid. CD39, CD73, and A2BR mimics/agonists alleviated lung and liver injury. Antagonists or the CD39, CD73, and A2BR knockout (KO) exacerbated lung injury, inflammatory cytokines, and chemokines as well as macrophage and neutrophil infiltration and accumulation in the lung. Agonists reduced the levels of the liver enzymes aspartate transferase and alanine transaminase in the blood, whereas antagonist administration or CD39, CD73, and A2BR KO enhanced enzyme levels. In addition, intestinal epithelial cell-specific deficient VillinCre-A2BRfl/fl mice showed increased intestinal injury compared to their wild-type VillinCre controls.

CONCLUSION

In conclusion, the CD39-CD73-A2BR axis protects against T/HS-induced multiple organ failure.

Adenosine A2A Receptor Activation Regulates Niemann-Pick C1 Expression and Localization in Macrophages

Adenosine plays an important role in modulating immune cell function, particularly T cells and myeloid cells, such as macrophages and dendritic cells. Cell surface adenosine A_2A receptors (A_2AR) regulate the production of pro-inflammatory cytokines and chemokines, as well as the proliferation, differentiation, and migration of immune cells. In the present study, we expanded the A_2AR interactome and provided evidence for the interaction between the receptor and the Niemann-Pick type C intracellular cholesterol transporter 1 (NPC1) protein. The NPC1 protein was identified to interact with the C-terminal tail of A_2AR in RAW 264.7 and IPMФ cells by two independent and parallel proteomic approaches. The interaction between the NPC1 protein and the full-length A_2AR was further validated in HEK-293 cells that permanently express the receptor and RAW264.7 cells that endogenously express A_2AR. A_2AR activation reduces the expression of NPC1 mRNA and protein density in LPS-activated mouse IPMФ cells. Additionally, stimulation of A_2AR negatively regulates the cell surface expression of NPC1 in LPS-stimulated macrophages. Furthermore, stimulation of A_2AR also altered the density of lysosome-associated membrane protein 2 (LAMP2) and early endosome antigen 1 (EEA1), two endosomal markers associated with the NPC1 protein. Collectively, these results suggested a putative A_2AR-mediated regulation of NPC1 protein function in macrophages, potentially relevant for the Niemann-Pick type C disease when mutations in NPC1 protein result in the accumulation of cholesterol and other lipids in lysosomes.

CD39/CD73/A2AR pathway and cancer immunotherapy

Cancer development is closely associated with immunosuppressive tumor microenvironment (TME) that attenuates antitumor immune responses and promotes tumor cell immunologic escape. The sequential conversion of extracellular ATP into adenosine by two important cell-surface ectonucleosidases CD39 and CD73 play critical roles in reshaping an immunosuppressive TME. The accumulated extracellular adenosine mediates its regulatory functions by binding to one of four adenosine receptors (A1R, A2AR, A2BR and A3R). The A2AR elicits its profound immunosuppressive function via regulating cAMP signaling. The increasing evidence suggests that CD39, CD73 and A2AR could be used as novel therapeutic targets for manipulating the antitumor immunity. In recent years, monoclonal antibodies or small molecule inhibitors targeting the CD39/CD73/A2AR pathway have been investigated in clinical trials as single agents or in combination with anti-PD-1/PD-L1 therapies. In this review, we provide an updated summary about the pathophysiological function of the adenosinergic pathway in cancer development, metastasis and drug resistance. The targeting of one or more components of the adenosinergic pathway for cancer therapy and circumvention of immunotherapy resistance are also discussed. Emerging biomarkers that may be used to guide the selection of CD39/CD73/A2AR-targeting treatment strategies for individual cancer patients is also deliberated.

Exploration of the link between gut microbiota and purinergic signalling

Growing evidence reveals that microorganisms in the gut are linked to metabolic health and disease risk in human beings to a considerable extent. The focus of research at this stage must tend to focus on cause-and-effect studies. In addition to being a component of DNA and RNA, purine metabolites can be involved in purine signalling in the body as chemical messengers. Abnormalities in purinergic signalling may lead to neuropathy, rheumatic immune diseases, inflammation, tumors, and a wide range of other diseases. It has proved that gut microbes are involved in purinergic signalling. The relationship between these gut-derived purinergic signalling molecules and host metabolism may be one of the important clues to our understanding of the mechanisms by which the microbiota affects host metabolism.

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.

CD73, a significant protein in liver diseases

Purine adenosine pathway exists widely in the body metabolism, and is involved in regulating various physiological processes. It is one of the important pathways of environmental regulation in human body. CD73 is essentially a protease that catalyzes further dephosphorylation of extracellular adenine nucleotides, hydrolyzing extracellular AMP to adenosine and phosphate. CD73 is an important part of the adenosine signaling pathway. Studies have shown that CD73-mediated adenosine pathway can convert the inflammatory ATP into the immunosuppressant adenosine. This paper aims to summarize the relevant effects of CD73 in the occurrence, development and prognosis of liver diseases such as viral hepatitis, highlight the important role of CD73 in liver diseases, especially in viral hepatitis such as HBV and HCV, and explore new clinical ideas for future treatment targets of liver diseases.

Nucleoside transporters and immunosuppressive adenosine signaling in the tumor microenvironment: Potential therapeutic opportunities

Adenosine compartmentalization has a profound impact on immune cell function by regulating adenosine localization and, therefore, extracellular signaling capabilities, which suppresses immune cell function in the tumor microenvironment. Nucleoside transporters, responsible for the translocation and cellular compartmentalization of hydrophilic adenosine, represent an understudied yet crucial component of adenosine disposition in the tumor microenvironment. In this review article, we will summarize what is known regarding nucleoside transporter's function within the purinome in relation to currently devised points of intervention (i.e., ectonucleotidases, adenosine receptors) for cancer immunotherapy, alterations in nucleoside transporter expression reported in cancer, and potential avenues for targeting of nucleoside transporters for the desired modulation of adenosine compartmentalization and action. Further, we put forward that nucleoside transporters are an unexplored therapeutic opportunity, and modulation of nucleoside transport processes could attenuate the pathogenic buildup of immunosuppressive adenosine in solid tumors, particularly those enriched with nucleoside transport proteins.

Extracellular adenosine induces hypersecretion of IL-17A by T-helper 17 cells through the adenosine A2a receptor

Extracellular adenosine, produced from ATP secreted by neuronal or immune cells, may play a role in endogenous regulation of inflammatory responses. Studies show that adenosine induces hypersecretion of IL-17A by CD4+ T cells upon treatment with an A2aR agonist (PSB0777), and that adenosine-mediated IL-17A hypersecretion is suppressed by the A2aR antagonist (Istradefylline) in humans. However, it is unclear whether A2aR downstream signaling is involved in IL-17A hypersecretion. Here, we show that inhibitors of adenyl cyclase (AC), protein kinase A (PKA), and cAMP response element binding protein (CREB) (which are signaling molecules downstream of the Gs protein coupled to the A2aR), suppress IL-17A production, suggesting that activation of A2aR signaling induces IL-17A production by CD4+ T cells. Furthermore, immune subset studies revealed that adenosine induces hypersecretion of IL-17A by T-helper (Th)17 cells. These results indicate that adenosine is an endogenous modulator of neutrophilic inflammation. Administration of an A2aR antagonist to mice with experimental autoimmune encephalomyelitis led to marked amelioration of symptoms. Thus, inhibitors of the novel A2aR-AC-cAMP-PKA-CREB signaling pathway for IL-17A hypersecretion by TCR-activated Th17 cells suppresses adenosine-mediated IL-17A production, suggesting that it may be an effective treatment for Th17-related autoimmune diseases.

CD4+CD25+ T regulatory cells in renal transplantation

The immune response to an allograft activates lymphocytes with the capacity to cause rejection. Activation of CD4+CD25+Foxp3+T regulatory cells (Treg) can down-regulate allograft rejection and can induce immune tolerance to the allograft. Treg represent <10% of peripheral CD4+T cells and do not markedly increase in tolerant hosts. CD4+CD25+Foxp3+T cells include both resting and activated Treg that can be distinguished by several markers, many of which are also expressed by effector T cells. More detailed characterization of Treg to identify increased activated antigen-specific Treg may allow reduction of non-specific immunosuppression. Natural thymus derived resting Treg (tTreg) are CD4+CD25+Foxp3+T cells and only partially inhibit alloantigen presenting cell activation of effector cells. Cytokines produced by activated effector cells activate these tTreg to more potent alloantigen-activated Treg that may promote a state of operational tolerance. Activated Treg can be distinguished by several molecules they are induced to express, or whose expression they have suppressed. These include CD45RA/RO, cytokine receptors, chemokine receptors that alter pathways of migration and transcription factors, cytokines and suppression mediating molecules. As the total Treg population does not increase in operational tolerance, it is the activated Treg which may be the most informative to monitor. Here we review the methods used to monitor peripheral Treg, the effect of immunosuppressive regimens on Treg, and correlations with clinical outcomes such as graft survival and rejection. Experimental therapies involving ex vivo Treg expansion and administration in renal transplantation are not reviewed.

A2A adenosine receptor activation prevents neutrophil aging and promotes polarization from N1 towards N2 phenotype

Extracellular adenosine is a biologically active signaling molecule that accumulates at sites of metabolic stress in sepsis. Extracellular adenosine has potent immunosuppressive effects by binding to and activating G protein-coupled A_2A adenosine receptors (A_2AARs) on the surface of neutrophils. A_2AAR signaling reproduces many of the phenotypic changes in neutrophils that are characteristic of sepsis, including decreased degranulation, impaired chemotaxis, and diminished ability to ingest and kill bacteria. We hypothesized that A_2AARs also suppress neutrophil aging, which precedes cell death, and N1 to N2 polarization. Using human neutrophils isolated from healthy subjects, we demonstrate that A_2AAR stimulation slows neutrophil aging, suppresses cell death, and promotes the polarization of neutrophils from an N1 to N2 phenotype. Using genetic knockout and pharmacological blockade, we confirmed that A_2AARs decrease neutrophil aging in murine sepsis induced by cecal ligation and puncture. A_2AARs expression is increased in neutrophils from septic patients compared to healthy subject but A_2AAR expression fails to correlate with aging or N1/N2 polarization. Our data reveals that A_2AARs regulate neutrophil aging in healthy but not septic neutrophils.

Recrystallization of Adenosine for Localized Drug Delivery

Adenosine (ADO) is an endogenous metabolite with immense potential to be repurposed as an immunomodulatory therapeutic, as preclinical studies have demonstrated in models of epilepsy, acute respiratory distress syndrome, and traumatic brain injury, among others. The currently licensed products Adenocard and Adenoscan are formulated at 3 mg/mL of ADO for rapid bolus intravenous injection, but the systemic administration of the saline formulations for anti-inflammatory purposes is limited by the nucleoside's profound hemodynamic effects. Moreover, concentrations that can be attained in the airway or the brain through direct instillation or injection are limited by the volumes that can be accommodated in the anatomical space (<5 mL in humans) and the rapid elimination by enzymatic and transport mechanisms in the interstitium (half-life <5 s). As such, highly concentrated formulations of ADO are needed to attain pharmacologically relevant concentrations at sites of tissue injury. Herein, we report a previously uncharacterized crystalline form of ADO (rcADO) in which 6.7 mg/mL of the nucleoside is suspended in water. Importantly, the crystallinity is not diminished in a protein-rich environment, as evidenced by resuspending the crystals in albumin (15% w/v). To the best of our knowledge, this is the first report of crystalline ADO generated using a facile and organic solvent-free method aimed at localized drug delivery. The crystalline suspension may be suitable for developing ADO into injectable formulations for attaining high concentrations of the endogenous nucleoside in inflammatory locales.

Roles of type 1 regulatory T (Tr1) cells in allergen-specific immunotherapy

Allergen-specific immunotherapy (AIT) is the only causative treatment for allergic diseases by modification of the immune response to allergens. A key feature of AIT is to induce immunotolerance to allergens by generating antigen-specific regulatory T (Treg) cells in allergic patients. Type 1 regulatory T (Tr1) cells and forkhead box protein 3 (Foxp3)-expressing Treg cells are well known among Treg cell subsets. Foxp3 was identified as a master transcription factor of Treg cells, and its expression is necessary for their suppressive activity. In contrast to Foxp3⁺ Treg cells, the master transcription factor of Tr1 cells has not been elucidated. Nevertheless, Tr1 cells are generally considered as a distinct subset of Treg cells induced in the periphery during antigen exposure in tolerogenic conditions and can produce large amounts of anti-inflammatory cytokines such as interleukin-10 and transforming growth factor-β, followed by down-regulation of the function of effector immune cells independently of Foxp3 expression. Since the discovery of Tr1 cells more than 20 years ago, research on Tr1 cells has expanded our understanding of the mechanism of AIT. Although the direct precursors and true identity of these cells continues to be disputed, we and others have demonstrated that Tr1 cells are induced in the periphery by AIT, and the induced cells are re-activated by antigens, followed by suppression of allergic symptoms. In this review, we discuss the immune mechanisms for the induction of Tr1 cells by AIT and the immune-suppressive roles of Tr1 cells in AIT.

The immunomodulatory function of adenosine in sepsis

Sepsis is an unsolved clinical condition with a substantial mortality rate in the hospital. Despite decades of research, no effective treatments for sepsis exists. The role of adenosine in the pathogenesis of sepsis is discussed in this paper. Adenosine is an essential endogenous molecule that activates the A1, A2a, A2b, and A3 adenosine receptors to regulate tissue function. These receptors are found on a wide range of immune cells and bind adenosine, which helps to control the immune response to inflammation. The adenosine receptors have many regulatory activities that determine the onset and progression of the disease, which have been discovered via the use of animal models. A greater understanding of the role of adenosine in modulating the immune system has sparked hope that an adenosine receptor-targeted treatment may be used one day to treat sepsis.

May be adenosine an immuno-quorum-sensing signal?

Quorum sensing indicates a communication process between bacteria based on a coordinate variation in gene expression aimed at coordinating a collective comportment related to the bacterial population density. Increasing pieces of evidence pointed out that a quorum-sensing system can be a regulatory program also used in the immune field to organize the density of the various immune cell populations and to calibrate their responses. In particular, such equilibrium is achieved by the ability of immune cells to perceive the density of their own populations or those of other cells in their environment, through the release of several mediators able to finely shape the cell density via coordinated changes in gene expression and protein signaling. In this regard, adenosine displays the typical characteristics of a mediator involved in the regulation of quorum sensing, thus suggesting a putative role of this nucleoside in shaping the balance between diverse immune cell populations.

The Effects of CD73 on Gastrointestinal Cancer Progression and Treatment

Gastrointestinal (GI) cancer is a common and deadly malignant tumor. CD73, a cell-surface protein, acts as a switch of the adenosine-related signaling pathway that can cause significant immunosuppression. Recent evidence has emerged that CD73 is a promising immunotherapy target for regaining immune cell function and restraining tumorigenesis, and a growing stream of research indicates that combining immunotherapy with other therapies can effectively improve the prognosis and survival of GI cancer patients. Several immune checkpoint inhibitors have been approved for use in GI cancer recently; however, they have demonstrated limited efficacy. Solving the problem of immunosuppression in GI cancer is the key to developing an effective therapeutic option and the modulation of CD73 expression may provide an answer. In this review, we discuss current research on CD73 in gastric, liver, pancreatic, and colorectal cancer to evaluate its therapeutic potential as an immunotherapy target in GI cancers.

Inosine and D-Mannose Secreted by Drug-Resistant Klebsiella pneumoniae Affect Viability of Lung Epithelial Cells

The antibiotic resistance rates of Klebsiella pneumoniae have been steadily increasing in recent years. Nevertheless, the metabolic features of the drug-resistant Klebsiella pneumoniae and its associated benefits for bacterial pathogenicity are far from expounded. This study aims to unravel the unique physiological and metabolic properties specific to drug-resistant K. pneumoniae. Using scanning electron microscopy (SEM), we observed a thicker extracellular mucus layer around a drug-resistant K. pneumonia strain (Kp-R) than a drug-sensitive K. pneumonia strain (Kp-S). Kp-R also produced more capsular polysaccharide (CPS) and biofilm, and appeared to have a significant competitive advantage when co-cultured with Kp-S. Moreover, Kp-R was easier to adhere to and invade A549 epithelial cells than Kp-S but caused less cell-viability damage according to cell counting kit-8 (CCK-8) tests. Immunofluorescence revealed that both Kp-R and Kp-S infection destroyed the tight junctions and F-actin of epithelial cells, while the damage caused by Kp-S was more severe than Kp-R. We detected the extracellular metabolites secreted by the two strains with UHPLC-Q-TOF MS to explore the critical secretion products. We identified 16 predominant compounds that were differentially expressed. Among them, inosine increased the viability of epithelial cells in a dose-dependent manner, and an A_2AR antagonist can abolish such enhancement. D-mannose, which was secreted less in Kp-R, inhibited the viability of A549 cells in the range of low doses. These findings provide potential targets and research strategies for preventing and treating drug-resistant K. pneumoniae infections.

Regionally selective cardiovascular responses to adenosine A2A and A2B receptor activation

Adenosine is a local mediator that regulates changes in the cardiovascular system via activation of four G protein-coupled receptors (A₁ , A_2A , A_2B , A₃ ). Here, we have investigated the effect of A_2A and A_2B -selective agonists on vasodilatation in three distinct vascular beds of the rat cardiovascular system. NanoBRET ligand binding studies were used to confirm receptor selectivity. The regional hemodynamic effects of adenosine A_2A and A_2B selective agonists were investigated in conscious rats. Male Sprague-Dawley rats (350-450 g) were chronically implanted with pulsed Doppler flow probes on the renal artery, mesenteric artery, and the descending abdominal aorta. Cardiovascular responses were measured following intravenous infusion (3 min for each dose) of the A_2A -selective agonist CGS 21680 (0.1, 0.3, 1 µg kg^-1 min^-1 ) or the A_2B -selective agonist BAY 60-6583 (4,13.3, 40 µg kg^-1 min^-1 ) following predosing with the A_2A -selective antagonist SCH 58261 (0.1 or 1 mg kg^-1 min^-1 ), the A_2B /A_2A antagonist PSB 1115 (10 mg kg^-1 min^-1 ) or vehicle. The A_2A -selective agonist CGS 21680 produced a striking increase in heart rate (HR) and hindquarters vascular conductance (VC) that was accompanied by a significant decrease in mean arterial pressure (MAP) in conscious rats. In marked contrast, the A_2B -selective agonist BAY 60-6583 significantly increased HR and VC in the renal and mesenteric vascular beds, but not in the hindquarters. Taken together, these data indicate that A_2A and A_2B receptors are regionally selective in their regulation of vascular tone. These results suggest that the development of A_2B receptor agonists to induce vasodilatation in the kidney may provide a good therapeutic approach for the treatment of acute kidney injury.

Adenosine Deaminase 1 Overexpression Enhances the Antitumor Efficacy of Chimeric Antigen Receptor-Engineered T Cells

Chimeric antigen receptor (CAR) T cell therapy mediates unprecedented benefit in certain leukemias and lymphomas, but has yet to achieve similar success in combating solid tumors. A substantial body of work indicates that the accumulation of adenosine in the solid tumor microenvironment (TME) plays a crucial role in abrogating immunotherapies. Adenosine deaminase 1 (ADA) catabolizes adenosine into inosine and is indispensable for a functional immune system. We have, for the first time, engineered CAR T cells to overexpress ADA. To potentially improve the pharmacokinetic profile of ADA, we have modified the overexpressed ADA in two ways, through the incorporation of a (1) albumin-binding domain or (2) collagen-binding domain. ADA and modified ADA were successfully expressed by CAR T cells and augmented CAR T cell exhaustion resistance. In a preclinical engineered ovarian carcinoma xenograft model, ADA and collagen-binding ADA overexpression significantly enhanced CAR T cell expansion, tumor tissue infiltration, tumor growth control, and overall survival, whereas albumin-binding ADA overexpression did not. Furthermore, in a syngeneic colon cancer solid tumor model, the overexpression of mouse ADA by cancer cells significantly reduced tumor burden and remodeled the TME to favor antitumor immunity. The overexpression of ADA for enhanced cell therapy is a safe, straightforward, reproducible genetic modification that can be utilized in current CAR T cell constructs to result in an armored CAR T product with superior therapeutic potential.

Adenosine receptor A2a blockade by caffeine increases IFN-gamma production in Th1 cells from patients with rheumatoid arthritis

OBJECTIVE

Studies indicate that caffeine uptake may be a risk factor for rheumatoid arthritis (RA), but a definitive link between caffeine consumption and RA has not been established. This study aimed to investigate the interplay between caffeine, adenosine receptor A2a, and interferon-γ (IFN-γ) production in CD4⁺ T cells from RA patients.

METHOD

Peripheral blood mononuclear cells were obtained from the peripheral blood of healthy individuals and patients with RA. CD4⁺ T cells were isolated using the magnetic activated cell sorting technique and cultured in vitro with caffeine or mock control. In addition, adenosine was used as a competitive inhibitor of caffeine. After 48 h, expression of IFN-γ and interleukin-17 (IL-17) was analysed by flow cytometry. Ex vivo expression levels of adenosine receptor A2a were also assessed.

RESULTS

Caffeine promoted IFN-γ production in Th1 cells in vitro. Significantly higher concentrations of caffeine were required to increase IFN-γ levels in Th1 cells from healthy individuals compared to Th1 cells from patients with RA. Moreover, ex vivo levels of adenosine receptor A2a expression on CD4⁺ T cells were significantly higher in RA than in healthy individuals. Caffeine-driven IFN-γ production was completely reversed by adenosine, a competitive agonist of adenosine receptor A2a. In contrast to IFN-γ, production of IL-17 was not affected by caffeine.

CONCLUSION

Caffeine promotes IFN-γ production in Th1 cells from RA patients in vitro by competitive inhibition of adenosine receptor A2a. Excessive coffee consumption could contribute to T-cell activation and inflammation in RA.

E-NTPDases: Possible Roles on Host-Parasite Interactions and Therapeutic Opportunities

Belonging to the GDA1/CD39 protein superfamily, nucleoside triphosphate diphosphohydrolases (NTPDases) catalyze the hydrolysis of ATP and ADP to the monophosphate form (AMP) and inorganic phosphate (Pi). Several NTPDase isoforms have been described in different cells, from pathogenic organisms to animals and plants. Biochemical characterization of nucleotidases/NTPDases has revealed the existence of isoforms with different specificities regarding divalent cations (such as calcium and magnesium) and substrates. In mammals, NTPDases have been implicated in the regulation of thrombosis and inflammation. In parasites, such as Trichomonas vaginalis, Trypanosoma spp., Leishmania spp., Schistosoma spp. and Toxoplasma gondii, NTPDases were found on the surface of the cell, and important processes like growth, infectivity, and virulence seem to depend on their activity. For instance, experimental evidence has indicated that parasite NTPDases can regulate the levels of ATP and Adenosine (Ado) of the host cell, leading to the modulation of the host immune response. In this work, we provide a comprehensive review showing the involvement of the nucleotidases/NTPDases in parasites infectivity and virulence, and how inhibition of NTPDases contributes to parasite clearance and the development of new antiparasitic drugs.

Purinergic receptor ligands: the cytokine storm attenuators, potential therapeutic agents for the treatment of COVID-19

The coronavirus disease-19 (COVID-19), at first, was reported in Wuhan, China, and then rapidly became pandemic throughout the world. Cytokine storm syndrome (CSS) in COVID-19 patients is associated with high levels of cytokines and chemokines that cause multiple organ failure, systemic inflammation, and hemodynamic instabilities. Acute respiratory distress syndrome (ARDS), a common complication of COVID-19, is a consequence of cytokine storm. In this regard, several drugs have been being investigated to suppress this inflammatory condition. Purinergic signaling receptors comprising of P1 adenosine and P2 purinoceptors play a critical role in inflammation. Therefore, activation or inhibition of some subtypes of these kinds of receptors is most likely to be beneficial to attenuate cytokine storm. This article summarizes suggested therapeutic drugs with potential anti-inflammatory effects through purinergic receptors.

Adenosine receptor ligation tips the uveitogenic Th1 and Th17 balance towards the latter in experimental autoimmune uveitis-induced mouse

Various pathological conditions are accompanied by release of adenosine triphosphate (ATP) from the intracellular to the extracellular compartment, where it degrades into adenosine and modulates immune responses. Previous studies concluded that both ATP and its degradation product adenosine are important immune-regulatory molecules; ATP acted as a danger signal that promotes immune responses, but adenosine's effect was inhibitory. We show that adenosine receptor ligation plays an important role in balancing Th1 and Th17 pathogenic T cell responses in experimental autoimmune uveitis (EAU). While its effect on Th1 responses is inhibitory, its effect on Th17 responses is enhancing, thereby impacting the balance between Th1 and Th17 responses. Mechanistic studies showed that this effect is mediated via several immune cells, among which γδ T cell activation and dendritic cell differentiation are prominent; adenosine- and γδ-mediated immunoregulation synergistically impact each other's effect. Adenosine receptor ligation augments the activation of γδ T cells, which is an important promoter for Th17 responses and has a strong effect on dendritic cell (DC) differentiation, tipping the balance from generation of DCs that stimulate Th1 responses to those that stimulate Th17 responses. The knowledge acquired in this study should improve our understanding of the immune-regulatory effect of extracellular ATP-adenosine metabolism and improve treatment for autoimmune diseases caused by both Th1-and Th17-type pathogenic T cells.

A novel definition and treatment of hyperinflammation in COVID-19 based on purinergic signalling

Hyperinflammation plays an important role in severe and critical COVID-19. Using inconsistent criteria, many researchers define hyperinflammation as a form of very severe inflammation with cytokine storm. Therefore, COVID-19 patients are treated with anti-inflammatory drugs. These drugs appear to be less efficacious than expected and are sometimes accompanied by serious adverse effects. SARS-CoV-2 promotes cellular ATP release. Increased levels of extracellular ATP activate the purinergic receptors of the immune cells initiating the physiologic pro-inflammatory immune response. Persisting viral infection drives the ATP release even further leading to the activation of the P2X7 purinergic receptors (P2X7Rs) and a severe yet physiologic inflammation. Disease progression promotes prolonged vigorous activation of the P2X7R causing cell death and uncontrolled ATP release leading to cytokine storm and desensitisation of all other purinergic receptors of the immune cells. This results in immune paralysis with co-infections or secondary infections. We refer to this pathologic condition as hyperinflammation. The readily available and affordable P2X7R antagonist lidocaine can abrogate hyperinflammation and restore the normal immune function. The issue is that the half-maximal effective concentration for P2X7R inhibition of lidocaine is much higher than the maximal tolerable plasma concentration where adverse effects start to develop. To overcome this, we selectively inhibit the P2X7Rs of the immune cells of the lymphatic system inducing clonal expansion of Tregs in local lymph nodes. Subsequently, these Tregs migrate throughout the body exerting anti-inflammatory activities suppressing systemic and (distant) local hyperinflammation. We illustrate this with six critically ill COVID-19 patients treated with lidocaine.

Novel classes of immunotherapy for breast cancer

Immune-checkpoint inhibitors have profoundly changed the treatment landscape for many tumor types. Despite marked improvements in disease control for highly immunogenic cancers, the clinical impact of checkpoint inhibitors in breast cancers to date is limited. Breast cancer is a heterogeneous disease with different levels of PD-L1 expression and variable tumor microenvironment (TME) composition according to molecular subtype. With emerging evidence of the role of different factors involved in immune evasion, there are promising new immunotherapy targets that will reshape early drug development for metastatic breast cancer. This review examines the available evidence for existing and emerging immuno-oncology (IO) approaches including small molecules targeting different regulators of the cancer-immunity cycle.

Extracellular ectonucleotidases are differentially regulated in murine tissues and human polymorphonuclear leukocytes during sepsis and inflammation

Sepsis is life-threatening organ dysfunction caused by a dysregulated inflammatory and immune response to infection. Sepsis involves the combination of exaggerated inflammation and immune suppression. During systemic infection and sepsis, the liver works as a lymphoid organ with key functions in regulating the immune response. Extracellular nucleotides are considered damage-associated molecular patterns and are involved in the control of inflammation. Their levels are finely tuned by the membrane-associated ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) enzyme family. Although previous studies have addressed the role of NTPDase1 (CD39), the role of the other extracellular NTPDases, NTPDase2, -3, and -8, in sepsis is unclear. In the present studies we identified NTPDase8 as a top downregulated gene in the liver of mice submitted to cecal ligation-induced sepsis. Immunohistochemical analysis confirmed the decrease of NTPDase8 expression at the protein level. In vitro mechanistic studies using HepG2 hepatoma cells demonstrated that IL-6 but not TNF, IL-1β, bacteria, or lipopolysaccharide are able to suppress NTPDase8 gene expression. NTPDase8, as well as NTPDase2 and NTPDase3 mRNA was downregulated, whereas NTPDase1 (CD39) mRNA was upregulated in polymorphonuclear leukocytes from both inflamed and septic patients compared to healthy controls. Although the host's inflammatory response of polymicrobial septic NTPDase8 deficient mice was no different from that of wild-type mice, IL-6 levels in NTPDase8 deficient mice were higher than IL-6 levels in wild-type mice with pneumonia. Altogether, the present data indicate that extracellular NTPDases are differentially regulated during sepsis.

Prognostic significance and immune correlates of CD73 expression in renal cell carcinoma

Background

CD73–adenosine signaling in the tumor microenvironment is immunosuppressive and may be associated with aggressive renal cell carcinoma (RCC). We investigated the prognostic significance of CD73 protein expression in RCC leveraging nephrectomy samples. We also performed a complementary analysis using The Cancer Genome Atlas (TCGA) dataset to evaluate the correlation of CD73 (ecto-5′-nucleotidase (NT5E), CD39 (ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1)) and A2 adenosine receptor (A2AR; ADORA2A) transcript levels with markers of angiogenesis and antitumor immune response.

Methods

Patients with RCC with available archived nephrectomy samples were eligible for inclusion. Tumor CD73 protein expression was assessed by immunohistochemistry and quantified using a combined score (CS: % positive cells×intensity). Samples were categorized as CD73_negative (CS=0), CD73_low or CD73_high (< and ≥median CS, respectively). Multivariable Cox regression analysis compared disease-free survival (DFS) and overall survival (OS) between CD73 expression groups. In the TCGA dataset, samples were categorized as low, intermediate and high NT5E, ENTPD1 and ADORA2A gene expression groups. Gene expression signatures for infiltrating immune cells, angiogenesis, myeloid inflammation, and effector T-cell response were compared between NT5E, ENTPD1 and ADORA2A expression groups.

Results

Among the 138 patients eligible for inclusion, ‘any’ CD73 expression was observed in 30% of primary tumor samples. High CD73 expression was more frequent in patients with M1 RCC (29% vs 12% M0), grade 4 tumors (27% vs 13% grade 3 vs 15% grades 1 and 2), advanced T-stage (≥T3: 22% vs T2: 19% vs T1: 12%) and tumors with sarcomatoid histology (50% vs 12%). In the M0 cohort (n=107), patients with CD73_high tumor expression had significantly worse 5-year DFS (42%) and 10-year OS (22%) compared with those in the CD73_negative group (DFS: 75%, adjusted HR: 2.7, 95% CI 1.3 to 5.9, p=0.01; OS: 64%, adjusted HR: 2.6, 95% CI 1.2 to 5.8, p=0.02) independent of tumor stage and grade. In the TCGA analysis, high NT5E expression was associated with significantly worse 5-year OS (p=0.008). NT5E and ENTPD1 expression correlated with higher regulatory T cell (Treg) signature, while ADORA2A expression was associated with increased Treg and angiogenesis signatures.

Conclusions

High CD73 expression portends significantly worse survival outcomes independent of stage and grade. Our findings provide compelling support for targeting the immunosuppressive and proangiogenic CD73–adenosine pathway in RCC.

Surface AMP deaminase 2 as a novel regulator modifying extracellular adenine nucleotide metabolism

Adenine nucleotides represent crucial immunomodulators in the extracellular environment. The ectonucleotidases CD39 and CD73 are responsible for the sequential catabolism of ATP to adenosine via AMP, thus promoting an anti-inflammatory milieu induced by the "adenosine halo". AMPD2 intracellularly mediates AMP deamination to IMP, thereby both enhancing the degradation of inflammatory ATP and reducing the formation of anti-inflammatory adenosine. Here, we show that this enzyme is expressed on the surface of human immune cells and its predominance may modify inflammatory states by altering the extracellular milieu. Surface AMPD2 (eAMPD2) expression on monocytes was verified by immunoblot, surface biotinylation, mass spectrometry, and immunofluorescence microscopy. Flow cytometry revealed enhanced monocytic eAMPD2 expression after TLR stimulation. PBMCs from patients with rheumatoid arthritis displayed significantly higher levels of eAMPD2 expression compared with healthy controls. Furthermore, the product of AMPD2-IMP-exerted anti-inflammatory effects, while the levels of extracellular adenosine were not impaired by an increased eAMPD2 expression. In summary, our study identifies eAMPD2 as a novel regulator of the extracellular ATP-adenosine balance adding to the immunomodulatory CD39-CD73 system.

Regulation of immune responses through CD39 and CD73 in cancer: Novel checkpoints

The immunosuppressive tumor microenvironment has been implicated in attenuating anti-tumoral immune responses and tumor growth in various cancers. Inhibitory immune checkpoints have been introduced as the primary culprits for developing the immunosuppressive tumor microenvironment. Therefore, a better understanding of the cross-talk between inhibitory immune checkpoints in the tumor microenvironment can pave the way for introducing novel approaches for treating affected patients. Growing evidence indicates that CD39 and CD73, as novel checkpoints, can transform adenosine triphosphate (ATP)-mediated pro-inflammatory tumor microenvironment into an adenosine-mediated immunosuppressive one via the purinergic signaling pathway. Indeed, enzymatic processes of CD39 and CD73 have crucial roles in adjusting the extent, intensity, and chemical properties of purinergic signals. This study aims to review the biological function of CD39 and CD73 and shed light on their significance in regulating anti-tumoral immune responses in various cancers.

Augmented Th17-stimulating activity of BMDCs as a result of reciprocal interaction between γδ and dendritic cells

Our previous studies demonstrated that γδ T cells have a strong regulatory effect on Th17 autoimmune responses in experimental autoimmune uveitis (EAU). In the current study, we show that reciprocal interactions between mouse γδ T cells and dendritic cells (DCs) played a major role in γδ regulation of Th17 responses. Mouse bone marrow-derived dendritic cells (BMDCs) acquired an increased ability to enhance Th17 autoimmune responses after exposure to γδ T cells; meanwhile, after exposure, a significant portion of the BMDCs expressed CD73 - a molecule that is fundamental in the conversion of immunostimulatory ATP into immunosuppressive adenosine. Functional studies showed that CD73+ BMDCs were uniquely effective in stimulating the Th17 responses, as compared to CD73- BMDCs; and activated γδ T cells are much more effective than non-activated γδ T cells at inducing CD73+ BMDCs. As a result, activated γδ T cells acquired greater Th17-enhancing activity. Treatment of BMDCs with the CD73-specific antagonist APCP abolished the enhancing effect of the BMDCs. γδ T cells more effectively induced CD73+ BMDCs from the BMDCs that were pre-exposed to TLR ligands, and the response was further augmented by adenosine. Moreover, BMDCs acquired increased ability to stimulate γδ activation after pre-exposure to TLR ligands and adenosine. Our results demonstrated that both extra-cellular adenosine and TLR ligands are critical factors in augmented Th17 responses in this autoimmune disease, and the reciprocal interactions between γδ T cells and DCs play a major role in promoting Th17 responses.

Limosilactobacillus reuteri and Lacticaseibacillus rhamnosus GG differentially affect gut microbes and metabolites in mice with Treg deficiency

Treg deficiency causes a lethal, CD4+ T cell-driven autoimmune disease called IPEX syndrome (immunodysregulation, polyendocrinopathy, and enteropathy, with X-linked inheritance) in humans and in the scurfy (SF) mouse, a mouse model of the disease. Feeding Limosilactobacillus reuteri DSM 17938 (LR 17938, LR) to SF mice reprograms the gut microbiota, reduces disease progression, and prolongs lifespan. However, the efficacy and mechanism of LR, compared with other probiotics, in producing these effects is unknown. We compared LR with Lacticaseibacillus rhamnosus GG (LGG), an extensively investigated probiotic. LR was more effective than LGG in prolonging survival. Both probiotics restored the fecal microbial alpha diversity, but they produced distinct fecal bacterial clusters and differentially modulated microbial relative abundance (RA). LR increased the RA of phylum_Firmicutes, genus_Oscillospira whereas LR reduced phylum_Bacteroidetes, genus_Bacteroides and genus_Parabacteroides, reversing changes attributed to the SF phenotype. LGG primarily reduced the RA of genus_Bacteroides. Both LR and LGG reduced the potentially pathogenic taxon class_γ-proteobacteria. Plasma metabolomics revealed substantial differences among 696 metabolites. We observed similar changes of many clusters of metabolites in SF mice associated with treatment with either LR or LGG. However, a unique effect of LR was to increase the abundance of plasma adenosine metabolites such as inosine, which we previously showed had immune modulatory effects. In conclusion: 1) different probiotics produce distinct signatures in the fecal microbial community in mice with Treg deficiency; and 2) when comparing different probiotics, there are strain-specific microbial products with different anti-inflammatory properties, reinforcing the concept that "one size does not fit all" in the treatment of autoimmune disease.NEW & NOTEWORTHY In the treatment of Treg-deficiency-induced autoimmunity, Limosilactobacillus reuteri DSM 17938 (LR) showed greater efficacy than Lacticaseibacillus rhamnosus GG (LGG). The study demonstrated that two different probiotics produce distinct signatures in the fecal microbial community in mice with Treg deficiency, but with many similarities in global plasma metabolites in general. However, there are strain-specific microbial products with different anti-inflammatory properties, reinforcing the concept that "one size does not fit all" in the treatment of autoimmune disease.

Ectonucleotidases in Inflammation, Immunity, and Cancer

Nucleoside triphosphate diphosphohydrolases (NTPDases) are a family of enzymes that hydrolyze nucleotides such as ATP, UTP, ADP, and UDP to monophosphates derivates such as AMP and UMP. The NTPDase family consists of eight enzymes, of which NTPDases 1, 2, 3, and 8 are expressed on cell membranes thereby hydrolyzing extracellular nucleotides. Cell membrane NTPDases are expressed in all tissues, in which they regulate essential physiological tissue functions such as development, blood flow, hormone secretion, and neurotransmitter release. They do so by modulating nucleotide-mediated purinergic signaling through P2 purinergic receptors. NTPDases 1, 2, 3, and 8 also play a key role during infection, inflammation, injury, and cancer. Under these conditions, NTPDases can contribute and control the pathophysiology of infectious, inflammatory diseases and cancer. In this review, we discuss the role of NTPDases, focusing on the less understood NTPDases 2-8, in regulating inflammation and immunity during infectious, inflammatory diseases, and cancer.

Release of adenosine-induced immunosuppression: Comprehensive characterization of dual A2A/A2B receptor antagonist

Immunosuppression is one of the main mechanisms facilitating tumor expansion. It may be driven by immune checkpoint protein expression, anti-inflammatory cytokine secretion or enhanced metabolic enzyme production, leading to the subsequent build-up of metabolites such as adenosine. Under physiological conditions, adenosine prevents the development of tissue damage resulting from a prolonged immune response; the same mechanism might be employed by tumor tissue to promote immunosuppression. Immune cells expressing A_2A and A_2B adenosine receptors present in an adenosine-rich environment have suppressed effector functions, such as cytotoxicity, proinflammatory cytokine release, antigen presentation and others, making them inert to cancer cells. This study was designed to investigate the dual antagonist potential of SEL330-639 to abolish adenosine-driven immunosuppression. SEL330-639 has slow dissociation kinetics. It inhibits cAMP production in human CD4⁺ cells, CD8⁺ cells and moDCs, which leads to diminished CREB phosphorylation and restoration of antitumor cytokine production (IL-2, TNFα, IL-12) in multiple primary human immune cells. The aforementioned results were additionally validated by gene expression analysis and functional assays in which NK cell line cytotoxicity was recovered by SEL330-639. Adenosine-driven immunosuppression is believed to preclude the effectiveness of immune checkpoint inhibitor therapies. Hence, there is an urgent need to develop new immuno-oncological strategies. Here, we comprehensively characterize SEL330-639, a novel dual A_2A/A_2B receptor antagonist effective in both lymphoid and myeloid cell populations with nanomolar potency. Due to its tight binding to the A_2A and A_2B receptors, this binding is sustained even at high adenosine concentrations mimicking the upper limit of the range of adenosine levels observed in the tumor microenvironment.

Intestinal microbiota: A potential target for enhancing the antitumor efficacy and reducing the toxicity of immune checkpoint inhibitors

Accumulating evidence suggests that the intestinal microbiota is associated with the antitumor efficacy of immune checkpoint inhibitors (ICIs) and the occurrence of immune-related adverse events (irAEs) following ICI treatment. However, the mechanisms underlying these interactions remain unclear. Recent technological advances have allowed more extensive investigation into the interplay between the intestinal microbiota and the tumor immune microenvironment. Breakthroughs by two research groups revealed that Bifidobacterium enhanced the efficacy of ICIs via the stimulator of interferon genes (STING) and adenosine 2A receptor (A_2AR) signaling pathways, highlighting the molecular mechanisms through which the intestinal microbiota modulates immunotherapy. In this review, we summarize recent findings related to the potential role and mechanisms of the gut microbiota in ICI therapy, available microbiota-targeting strategies, and ongoing clinical trials. Further we discuss the associated challenges that remain in this field of research. The current review aims to evaluate the potential of the intestinal microbiota in maximizing the antitumor efficacy of ICIs while minimizing their toxic effects and guiding the development of more specific treatment regimens.

Conversion of ATP to adenosine by CD39 and CD73 in multiple myeloma can be successfully targeted together with adenosine receptor A2A blockade

Background

PD1/PDL1-directed therapies have been unsuccessful for multiple myeloma (MM), an incurable cancer of plasma cells in the bone marrow (BM). Therefore, other immune checkpoints such as extracellular adenosine and its immunosuppressive receptor should be considered. CD39 and CD73 convert extracellular ATP to adenosine, which inhibits T-cell effector functions via the adenosine receptor A2A (A2AR). We set out to investigate whether blocking the adenosine pathway could be a therapy for MM.

Methods

Expression of CD39 and CD73 on BM cells from patients and T-cell proliferation were determined by flow cytometry and adenosine production by Liquid chromatograpy-mass spectrometry (HPCL/MS). ENTPD1 (CD39) mRNA expression was determined on myeloma cells from patients enrolled in the publicly available CoMMpass study. Transplantable 5T33MM myeloma cells were used to determine the effect of inhibiting CD39, CD73 and A2AR in mice in vivo.

Results

Elevated level of adenosine was found in BM plasma of MM patients. Myeloma cells from patients expressed CD39, and high gene expression indicated reduced survival. CD73 was found on leukocytes and stromal cells in the BM. A CD39 inhibitor, POM-1, and an anti-CD73 antibody inhibited adenosine production and reduced T-cell suppression in vitro in coculture of myeloma and stromal cells. Blocking the adenosine pathway in vivo with a combination of Sodium polyoxotungstate (POM-1), anti-CD73, and the A2AR antagonist AZD4635 activated immune cells, increased interferon gamma production, and reduced the tumor load in a murine model of MM.

Conclusions

Our data suggest that the adenosine pathway can be successfully targeted in MM and blocking this pathway could be an alternative to PD1/PDL1 inhibition for MM and other hematological cancers. Inhibitors of the adenosine pathway are available. Some are in clinical trials and they could thus reach MM patients fairly rapidly.

The role of P2Y receptors in regulating immunity and metabolism

P2Y receptors are G protein-coupled receptors whose physiological agonists are the nucleotides ATP, ADP, UTP, UDP and UDP-glucose. Eight P2Y receptors have been cloned in humans: P2Y₁R, P2Y₂R, P2Y₄R, P2Y₆R, P2Y₁₁R, P2Y₁₂R, P2Y₁₃R and P2Y₁₄R. P2Y receptors are expressed in lymphoid tissues such as thymus, spleen and bone marrow where they are expressed on lymphocytes, macrophages, dendritic cells, neutrophils, eosinophils, mast cells, and platelets. P2Y receptors regulate many aspects of immune cell function, including phagocytosis and killing of pathogens, antigen presentation, chemotaxis, degranulation, cytokine production, and lymphocyte activation. Consequently, P2Y receptors shape the course of a wide range of infectious, autoimmune, and inflammatory diseases. P2Y₁₂R ligands have already found their way into the therapeutic arena, and we envision additional ligands as future drugs for the treatment of diseases caused by or associated with immune dysregulation.

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.