Hydrolysis of extracellular ATP and immune suppression: humans versus mice

Delivery of an ectonucleotidase inhibitor with ROS-responsive nanoparticles overcomes adenosine-mediated cancer immunosuppression

Tumor evasion of immune destruction is associated with the production of immunosuppressive adenosine in the tumor microenvironment (TME). Anticancer therapies can trigger adenosine triphosphate (ATP) release from tumor cells, causing rapid formation of adenosine by the ectonucleotidases CD39 and CD73, thereafter exacerbating immunosuppression in the TME. The goal of this study was to develop an approach to facilitate cancer therapy-induced immunogenic cell death including ATP release and to limit ATP degradation into adenosine, in order to achieve durable antitumor immune response. Our approach was to construct reactive oxygen species (ROS)-producing nanoparticles that carry an ectonucleotidase inhibitor ARL67156 by electronic interaction and phenylboronic ester. Upon near-infrared irradiation, nanoparticle-produced ROS induced ATP release from MOC1 cancer cells in vitro and triggered the cleavage of phenylboronic ester, facilitating the release of ARL67156 from the nanoparticles. ARL67156 prevented conversion of ATP to adenosine and enhanced anticancer immunity in an MOC1-based coculture model. We tested this approach in mouse tumor models. Nanoparticle-based ROS-responsive drug delivery reprogramed the immunogenic landscape in tumors, eliciting tumor-specific T cell responses and tumor regression, conferring long-term survival in mouse models. We demonstrated that TME reprograming sets the stage for response to anti-programmed cell death protein 1 (PD1) immunotherapy, and the combination resulted in tumor regression in a 4T1 breast cancer mouse model that was resistant to PD1 blockade. Furthermore, our approach also induced immunological effects in patient-derived organotypic tumor spheroid model, suggesting potential translation of our nanoparticle approach for treating human cancers.

Human ectoenzyme-expressing ILC3: immunosuppressive innate cells that are depleted in graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is often associated with chemotherapy- and radiotherapy-induced host tissue damage, leading to graft-versus-host disease (GVHD). Innate lymphoid cells (ILC) have an essential role in tissue homeostasis and tissue repair via their production of interleukin (IL)-22, which acts on intestinal stem cells. The tissue healing capacities of ILC via IL-22 in the context of allo-HSCT and GVHD has previously been demonstrated in a mouse model for acute GVHD. We investigated potential other ways of ILC-mediated tissue protection against GVHD. Tissue injury leads to the release of danger-associated molecular patterns (DAMPs). DAMPs interact with purinergic receptors and ectoenzymes on immune cells and induce pleiotropic effects, including activation of proinflammatory antigen-presenting cells and immunosuppressive effects via the generation of adenosine. Here, we report a novel subset of human ILC3 that coexpress the ectoenzymes CD39 and CD73 (ecto+ ILC3). Ecto+ ILC3 express RORγt and were present in the oral-gastrointestinal tract and bone marrow. ILC3 ectoenzyme expression is modulated by the proinflammatory cytokine IL-1β. Extracellular adenosine triphosphate (eATP) stimulated ecto+ ILC3 to produce IL-22 and adenosine. Activated ecto+ ILC3 suppressed autologous T-cell proliferation in coculture experiments via the production of adenosine. In allo-HSCT recipients, intestinal GVHD was associated with reduced proportions of ecto+ ILC3 and decreased levels of adenosine and its metabolite inosine. Taken together, ecto+ ILC3 have immunosuppressive properties, but in patients with GVHD, ecto+ ILC3 are depleted. A lack of ecto+ ILC3 and subsequent reduced capacity to neutralize DAMPs may contribute to the development of GVHD.

ATP-evoked sustained vasoconstrictions mediated by heteromeric P2X1/4 receptors in cerebral arteries

BACKGROUND AND PURPOSE

Current knowledge states that vasoconstrictor responses to ATP are mediated by rapidly desensitizing ligand-gated P2X1 receptors in vascular smooth muscle cells (VSMCs). However, ATP is implicated in contributing to pathological conditions involving sustained vasoconstrictor response such as cerebral vasospasm. The purpose of this study is to test the hypothesis that the stimulation of VSMC P2XR receptors (P2XRs) contributes to ATP-evoked sustained vasoconstrictions in rat middle cerebral arteries (RMCAs).

METHODS

Reverse transcription- polymerase chain reaction, Western blot, and immunocytochemistry were used to analyze expression of mRNA and proteins in RMCAs VSMCs. Ionic currents and calcium responses were investigated using patch-clamp and confocal imaging techniques, respectively. Functional responses were confirmed using wire myography.

RESULTS

Expression of mRNA and protein for P2X1R and P2X4R subunits was identified in RMCA VSMCs. Confocal imaging in fluo-3-loaded VSMCs showed that ATP and a selective P2XR agonist, αβmeATP, evoked similar dose-dependent increases in [Ca(2+)]i. Patch-clamp experiments identified 2 components of P2XR-mediated currents: consisting of a fast desensitizing phase mediated by homomeric P2X1Rs and a slowly desensitizing phase involving heteromeric P2X1/4Rs. Isometric tension measurements showed that ≈80%:20% of initial ATP-evoked vasoconstriction in RMCA is mediated by homomeric P2X1Rs and heteromeric P2X1/4Rs, respectively. The sustained slowly desensitizing and rapidly recovering from desensitization responses are mediated by heteromeric P2X1/4Rs.

CONCLUSIONS

This study reveals for the first time that apart from rapidly desensitizing homomeric P2X1Rs, heteromeric P2X1/4Rs contribute to the sustained component of the purinergic-mediated vasoconstriction in RMCA. Our study, therefore, identifies possible novel targets for therapeutical intervention in cerebral circulation.

The arginine kinase in Zhikong scallop Chlamys farreri is involved in immunomodulation

Arginine kinase (AK) catalyzes the reversible phosphorylation of l-arginine to form phosphoarginine, and plays a critical role in energy metabolism in invertebrates. In the present study, a scallop AK gene was identified from Chlamys farreri with an open reading frame (ORF) of 1101bp encoding for a protein of 366 amino acids (designed as CfAK). An ATP-gua PtransN domain which was described as a guanidine substrate specificity domain (GS domain) and an ATP-gua Ptrans domian which was responsible for binding ATP, were both identified in CfAK. The mRNA transcripts of CfAK were detectable in haemocytes, hepatopancreas, adductor muscle, mantle, gill, kidney and gonad, with the highest expression level in the muscle and the lowest level in the hemocytes. The expression level of CfAK mRNA increased from fertilized eggs to eyebot, and reached the highest in the trochophore stage. The relative expression level of CfAK mRNA in muscle was up-regulated significantly after LPS (0.5mg/mL) stimulation, and reached the peak at 6h (5.2-fold, P<0.05). The activity of inducible nitric oxide synthase (iNOS) in the supernatant of muscle homogenate increased significantly from 3.2U/mg at 0 h to 9.7 U/mg at 12h after LPS stimulation, while the concentration of nitric oxide (NO) in the supernatant of muscle homogenate began to increase at 3h (21.55 μmol/L), and reached the top concentration at 24h (42.27 μmol/L), then recovered to the normal level after 48 h. The recombinant protein of CfAK (rCfAK) expressed in Escherichia coli displayed Arginine kinase activity, and its apparent K(m) was 0.82 ± 0.11 and 1.24 ± 0.13 mM for L-arginine and ATP-Na, respectively. The results indicated that the CfAK was involved in energy production and utilization during the whole life process, and might refer to the immunomodulation process via altering the NO concentration and iNOS activity in scallop Chlamys farreri.

The therapeutic potential of adenosine triphosphate as an immune modulator in the treatment of HIV/AIDS: a combination approach with HAART

Extracellular adenosine triphosphate (eATP) is a potent molecule that has the capacity to modulate various aspects of cell functions including gene expression. This element of modulation is essential to the role of ATP as a therapeutic agent. The hypothesis presented is that ATP can have an important impact on the treatment of HIV infection. This is supported in part by published research, although a much greater role for ATP is suggested than prior authors ever thought possible. ATP has the ability to enhance the immune system and could thus improve the host's own defense mechanisms to eradicate the virus-infected cells and restore normal immune function. This could provide effective therapy when used in conjunction with highly active antiretroviral therapies (HAART) to eliminate the latently infected cells. The key lies in applying ATP through the methodology described. This article presents a strategy for using ATP therapeutically along with background evidence to substantiate the importance of using ATP in the treatment of HIV infection.

High expression of the ectonucleotidase CD39 on T cells from the inflamed site identifies two distinct populations, one regulatory and one memory T cell population

The ectonucleotidase CD39 has recently been described as being highly expressed on regulatory Foxp3(+) CD4 T cells. Through hydrolysis of proinflammatory extracellular ATP, CD39 activity represents a newly described mechanism of regulatory T cell action. We report a novel population of human CD4 T cells that express CD39 yet are Foxp3 negative. These cells produce the proinflammatory cytokines IFN-gamma and IL-17 and fail to suppress proliferation; however, they still have high ATP hydrolysis activity. In the inflammatory site in human juvenile idiopathic arthritis, the CD39(+)Foxp3(-) population is greatly increased compared with peripheral blood of patients or healthy controls. We also show that cells expressing the AMPase CD73 are less frequent in the joint than in blood. To our knowledge, this is the first study to describe and characterize CD39 function on CD4 T cells from the target site in a human autoinflammatory condition. Our data suggest that in human CD4(+) T cells from the inflamed site, CD39 can be highly expressed on two populations, one regulatory and the other of a memory phenotype.

Self-regulation of inflammatory cell trafficking in mice by the leukocyte surface apyrase CD39

Leukocyte and platelet accumulation at sites of cerebral ischemia exacerbate cerebral damage. The ectoenzyme CD39 on the plasmalemma of endothelial cells metabolizes ADP to suppress platelet accumulation in the ischemic brain. However, the role of leukocyte surface CD39 in regulating monocyte and neutrophil trafficking in this setting is not known. Here we have demonstrated in mice what we believe to be a novel mechanism by which CD39 on monocytes and neutrophils regulates their own sequestration into ischemic cerebral tissue, by catabolizing nucleotides released by injured cells, thereby inhibiting their chemotaxis, adhesion, and transmigration. Bone marrow reconstitution and provision of an apyrase, an enzyme that hydrolyzes nucleoside tri- and diphosphates, each normalized ischemic leukosequestration and cerebral infarction in CD39-deficient mice. Leukocytes purified from Cd39-/- mice had a markedly diminished capacity to phosphohydrolyze adenine nucleotides and regulate platelet reactivity, suggesting that leukocyte ectoapyrases modulate the ambient vascular nucleotide milieu. Dissipation of ATP by CD39 reduced P2X7 receptor stimulation and thereby suppressed baseline leukocyte alphaMbeta2-integrin expression. As alphaMbeta2-integrin blockade reversed the postischemic, inflammatory phenotype of Cd39-/- mice, these data suggest that phosphohydrolytic activity on the leukocyte surface suppresses cell-cell interactions that would otherwise promote thrombosis or inflammation. These studies indicate that CD39 on both endothelial cells and leukocytes reduces inflammatory cell trafficking and platelet reactivity, with a consequent reduction in tissue injury following cerebral ischemic challenge.