Regulatory T cells in transplantation: does extracellular adenosine triphosphate metabolism through CD39 play a crucial role?

Novel potential therapeutic targets of alopecia areata

Alopecia areata (AA) is a non-scarring hair loss disorder caused by autoimmunity. The immune collapse of the hair follicle, where interferon-gamma (IFN-γ) and CD8+ T cells accumulate, is a key factor in AA. However, the exact functional mechanism remains unclear. Therefore, AA treatment has poor efficacy maintenance and high relapse rate after drug withdrawal. Recent studies show that immune-related cells and molecules affect AA. These cells communicate through autocrine and paracrine signals. Various cytokines, chemokines and growth factors mediate this crosstalk. In addition, adipose-derived stem cells (ADSCs), gut microbiota, hair follicle melanocytes, non-coding RNAs and specific regulatory factors have crucial roles in intercellular communication without a clear cause, suggesting potential new targets for AA therapy. This review discusses the latest research on the possible pathogenesis and therapeutic targets of AA.

The Association between Regulatory T Cell Subpopulations and Severe Pneumonia Post Renal Transplantation

Severe pneumonia accounts for the majority of morbidity and mortality in renal allograft recipients due to immunosuppressant maintenance. Regulatory T cells (Tregs), which are involved in tackling infections under immunosuppressive conditions, are rarely uncovered. We aimed to investigate the relationship between various Treg subpopulations and severe pneumonia after kidney transplantation (KTx). KTx recipients with pneumonia were divided into severe pneumonia and mild pneumonia groups. The frequencies and absolute numbers (Ab No.) of total Tregs (CD4+CD25+FoxP3+), six subsets of Tregs (Helios+/-, CD39+/-, and CD45RA+/-), and T cells, B cells, and NK cells were assessed from peripheral blood via flow cytometry using the $t$ or Mann-Whitney test and receiver operating curve analysis. We also determined the median fluorescence intensity (MFI) of human leukocyte antigen- (HLA-) DR on monocytes and CD64 on neutrophils. Logistic regression was used to identify the risk factors of disease progression, and Pearson’s correlation analysis was performed to identify relationships between the measured immune indices and patients’ clinical information. Our research indicated that Treg subpopulations were strongly associated with severe pneumonia progression post KTx. Based on the monitoring of Treg subpopulations, better-individualized prevention and therapy might be achieved for patients with severe pneumonia post KTx.

Everolimus-Induced Immune Effects after Heart Transplantation: A Possible Tool for Clinicians to Monitor Patients at Risk for Transplant Rejection

Background: Patients treated with an inhibitor of the mechanistic target of rapamycin (mTORI) in a calcineurin inhibitor (CNI)-free immunosuppressive regimen after heart transplantation (HTx) show a higher risk for transplant rejection. We developed an immunological monitoring tool that may improve the identification of mTORI-treated patients at risk for rejection. Methods: Circulating dendritic cells (DCs) and regulatory T cells (T_regs) were analysed in 19 mTORI- and 20 CNI-treated HTx patients by flow cytometry. Principal component and cluster analysis were used to identify patients at risk for transplant rejection. Results: The percentages of total T_regs (p = 0.02) and CD39⁺ T_regs (p = 0.05) were higher in mTORI-treated patients than in CNI-treated patients. The principal component analysis revealed that BDCA1⁺, BDCA2⁺ and BDCA4⁺ DCs as well as total T_regs could distinguish between non-rejecting and rejecting mTORI-treated patients. Most mTORI-treated rejectors showed higher levels of BDCA2⁺ and BDCA4⁺ plasmacytoid DCs and lower levels of BDCA1⁺ myeloid DCs and T_regs than mTORI non-rejectors. Conclusion: An mTORI-based immunosuppressive regimen induced a sufficient, tolerance-promoting reaction in T_regs, but an insufficient, adverse effect in DCs. On the basis of patient-specific immunological profiles, we established a flow cytometry-based monitoring tool that may be helpful in identifying patients at risk for rejection.

Extracellular adenosine reversibly inhibits the activation of human regulatory T cells and negatively influences the achievement of the operational tolerance in liver transplantation

The artificial induction of tolerance in transplantation is gaining strength. In mice, a differential role of extracellular adenosine (eADO) for regulatory and effector T cells (Tregs and Teffs, respectively) has been proposed: inhibiting Teffs and inducing Tregs. The aim of this study was to analyze the action of extracellular nucleotides in human T cells and, moreover, to examine the influence of CD39 and CD73 ectonucleotidases and subsequent adenosine signaling through adenosine 2 receptor (A₂ R) in the induction of clinical tolerance after liver transplant. The action of extracellular nucleotides in human T cells was analyzed by in vitro experiments with isolated T cells. Additionally, 17 liver transplant patients were enrolled in an immunosuppression withdrawal trial, and the differences in the CD39-CD73-A₂ R axis were compared between tolerant and nontolerant patients. In contrast to the mice, the activation of human Tregs was inhibited similarly to Teffs in the presence of eADO. Moreover, the expression of the enzyme responsible for the degradation of ADO, adenosine deaminase, was higher in tolerant patients with respect to the nontolerant group along the immunosuppression withdrawal. Our data support the idea that eADO signaling and its degradation may play a role in the complex system of regulation of liver transplant tolerance.

Regulation of the Immune Response by the Inflammatory Metabolic Microenvironment in the Context of Allotransplantation

Antigen challenge induced by allotransplantation results in the activation of T and B cells, followed by their differentiation and proliferation to mount an effective immune response. Metabolic fitness has been shown to be crucial for supporting the major shift from quiescent to active immune cells and for tuning the immune response. Metabolic reprogramming includes regulation of the balance between glycolysis and mitochondrial respiration processes. Recent research has shed new light on the functions served by the end products of metabolism such as lactate, acetate, and ATP. At enhanced local concentrations, these metabolites have complex effects in which they not only induce T and B cell responses, cell mobility, and cytokine secretion but also favor the resolution of inflammation by promoting regulatory functions. Such mechanisms are instrumental in the context of the immune response in transplantation, not only to protect the graft and/or eliminate cells targeting it but also to maintain cell homeostasis per se. Metabolic adaptation thus plays an instrumental role on the outcome of the cellular and humoral responses. This, of course, raises the possibility of drugs that would interfere in these metabolic pathways to control the immune response but also highlights the risk that some drugs may perturb this metabolism and cell homeostasis and be deleterious for graft outcome. This review focuses on how metabolic alterations of the local immune microenvironment regulate the immune response and the impact of metabolic manipulation in allotransplantation.

CD39-adenosinergic axis in renal pathophysiology and therapeutics

Extracellular ATP interacts with purinergic type 2 (P2) receptors and elicits many crucial biological functions. Extracellular ATP is sequentially hydrolyzed to ADP and AMP by the actions of defined nucleotidases, such as CD39, and AMP is converted to adenosine, largely by CD73, an ecto-5'-nucleotidase. Extracellular adenosine interacts with P1 receptors and often opposes the effects of P2 receptor activation. The balance between extracellular ATP and adenosine in the blood and extracellular fluid is regulated chiefly by the activities of CD39 and CD73, which constitute the CD39-adenosinergic axis. In recent years, several studies have shown this axis to play critical roles in transport of water/sodium, tubuloglomerular feedback, renin secretion, ischemia reperfusion injury, renal fibrosis, hypertension, diabetic nephropathy, transplantation, inflammation, and macrophage transformation. Important developments include global and targeted gene knockout and/or transgenic mouse models of CD39 or CD73, biological or small molecule inhibitors, and soluble engineered ectonucleotidases to directly impact the CD39-adenosinergic axis. This review presents a comprehensive picture of the multiple roles of CD39-adenosinergic axis in renal physiology, pathophysiology, and therapeutics. Scientific advances and greater understanding of the role of this axis in the kidney, in both health and illness, will direct development of innovative therapies for renal diseases.

Increased degradation of ATP is driven by memory regulatory T cells in kidney transplantation tolerance

Regulatory T cells were recently proposed as the central actor in operational tolerance after renal transplantation. Tolerant patients harbor increased FoxP3hi memory Treg frequency and increased demethylation in the Foxp3 Treg-specific demethylated region when compared to stable kidney recipients and exhibit greater memory Treg suppressive capacities and higher expression of the ectonucleotidase CD39. However, in this particular and unique situation the mechanisms of action of Tregs were not identified. Thus, we analyzed the ability of memory Tregs to degrade extracellular ATP in tolerant patients, healthy volunteers, and patients with stable graft function under immunosuppression and determined the role of immunosuppressive drugs on this process. The conserved proportion of memory Tregs leads to the establishment of a pro-tolerogenic balance in operationally tolerant patients. Memory Tregs in tolerant patients display normal capacity to degrade extracellular ATP/ADP. In contrast, memory Tregs from patients with stable graft function do not have this ability. Finally, in vitro, immunosuppressive drugs may favor the lower proportion of memory Tregs in stable patients, but they have no effect on CD39-dependent ATP degradation and do not explain memory Treg lack of extracellular ATP/ADP degradation ability. Thus, intrinsic active regulatory mechanisms may act long after immunosuppressive drug arrest in operationally tolerant patients and may contribute to kidney allograft tolerance via the maintenance of CD39 Treg function.

Extracellular ATP signaling and clinical relevance

Since purinergic signaling was discovered in the early 1970s, it has been shown that extracellular nucleotides, and their derivative nucleosides, are released in a regulated or unregulated manner by cells in various challenging settings and then bind defined purinergic receptors to activate intricate signaling networks. Extracellular ATP plays a role based on different P2 receptor subtypes expressed on specific cell types. Sequential hydrolysis of extracellular ATP catalyzed by ectonucleotidases (e.g. CD39, CD73) is the main pathway for the generation of adenosine, which in turn activates P1 receptors. Many studies have demonstrated that extracellular ATP signaling functions as an important dynamic regulatory pathway to coordinate appropriate immune responses in various pathological processes, including intracellular infection, host-tumor interaction, pro-inflammation vascular injury, and transplant immunity. ATP receptors and CD39 also participate in related clinical settings. Here, we review the latest research in to the development of promising clinical treatment strategies.

Ex vivo-expanded baboon CD39 + regulatory T cells prevent rejection of porcine islet xenografts in NOD-SCID IL-2rγ-/- mice reconstituted with baboon peripheral blood mononuclear cells

BACKGROUND

A high immunosuppressive burden is required for long-term islet xenograft survival in non-human primates even using genetically modified donor pigs.

AIMS

We aimed to investigate the capacity of baboon regulatory T cells (Treg) to suppress islet xenograft rejection, thereby developing a potential immunoregulatory or tolerance therapy that could be evaluated in NHP models of xenotransplantation.

MATERIALS & METHODS

Baboon Treg expanded with stimulation by porcine peripheral blood mononuclear cells (PBMC) were characterized by cell phenotyping and suppressive activity assays in vitro. Their function in vivo was evaluated in neonatal porcine islet cell clusters (NICC) transplanted NOD-SCID IL-2rγ-/- (NSG) mice receiving baboon PBMC alone or with expanded autologous Treg.

RESULTS

The majority of expanded Treg coexpressed Foxp3 and CD39 and were highly suppressive of the baboon anti-pig xenogeneic T cell response in vitro. Reconstitution of mice with baboon PBMC alone resulted in NICC xenograft rejection within 35 days. Cotransfer with baboon PBMC and Treg prolonged islet xenograft survival beyond 100 days, correlating with Treg engraftment, intragraft CD39 and Foxp3 gene expression, and reduced graft infiltrating effector T cells and reduced interferon-γ production.

DISCUSSION & CONCLUSION

Our data supports the capacity of ex vivo expanded CD39+ baboon Treg to suppress islet xenograft rejection in primatized mice, suggesting it has potential as an adjunctive immunotherapy in preclinical NHP models of xenotransplantation.

CD39+ regulatory T cells attenuate allergic airway inflammation

BACKGROUND

The suppressive mechanism of regulatory T cells (Tregs) has remained incompletely clarified. Recent studies found that CD39 expressed by Tregs may participate in the immunoregulatory role of Tregs. CD39-induced ATP hydrolysis and/or adenosine generation contribute to the suppressive mechanism of Tregs. Previous studies suggested that ATP is involved in allergic airway inflammation by acting on type 2 purinergic (P2) receptors, but the role of CD39 and CD39(+) Tregs in allergic airway inflammation has not been elaborated.

OBJECTIVE

To investigate the role and underlying mechanism of CD39 expression by Tregs in allergic airway inflammation.

METHODS

A model of allergic asthma was developed with ovalbumin-alum in female Cd39 wild type (Cd39(+/+) ) and deficient (Cd39(-/-) ) C57BL/6 mice. Foxp3-GFP knock-in Cd39(+/+) and Cd39(-/-) mice were used to sort CD4(+) GFP(+) cells (Tregs) for exploring the role of CD39 expression by Tregs in allergic asthma. The effects of modulating CD39 activity with ARL67156 (inhibitor) or apyrase were also observed.

RESULTS

ARL67156 greatly worsened airway inflammation including increased lung inflammatory cells infiltration, goblet cell hyperplasia, and higher levels of Th2 and Th17 cytokines in bronchoalveolar lavage fluid (BALF), accompanied by an increment in transcription factor (GATA-3 and RORγt) and P2R (P2Y2, P2Y4 and P2Y6) mRNA expression in lungs. This potentiating effect was rescued by intratracheal injection of apyrase. Airway inflammation was markedly increased in Cd39(-/-) mice compared to Cd39(+/+) mice. In contrast to CD39(-) Tregs, CD39(+) Tregs showed stronger suppressive effects on airway inflammation. In vitro suppression assay suggested that CD39(+) Tregs have more potent suppressive effect on cytokines secretion from CD4(+) CD25(-) responder T cells and the inhibitory effects were reduced by addition of adenosine A2A receptor antagonist.

CONCLUSION

CD39 expressed on Tregs participates in the regulation of limiting allergic airway inflammation by regulating extracellular ATP and/or adenosine. CD39 may represent a new therapeutic target for asthma.

CD73 and CD39 ectonucleotidases in T cell differentiation: Beyond immunosuppression

Extracellular ATP is a danger signal released by dying and damaged cells, and it functions as an immunostimulatory signal that promotes inflammation. However, extracellular adenosine acts as an immunoregulatory signal that modulates the function of several cellular components of the adaptive and innate immune response. Consequently, the balance between ATP and adenosine concentration is crucial in immune homeostasis. CD39 and CD73 are two ectonucleotidases that cooperate in the generation of extracellular adenosine through ATP hydrolysis, thus tilting the balance towards immunosuppressive microenvironments. Extracellular adenosine can prevent activation, proliferation, cytokine production and cytotoxicity in T cells through the stimulation of the A2A receptor; however, recent evidence has shown that adenosine may also affect other processes in T-cell biology. In this review, we discuss evidence that supports a role of CD73 and CD39 ectonucleotidases in controlling naive T-cell homeostasis and memory cell survival through adenosine production. Finally, we propose a novel hypothesis of a possible role of these ectonucleotidases and autocrine adenosine signaling in controlling T-cell differentiation.

Extracorporeal photopheresis after heart transplantation

The addition of extracorporeal photopheresis (ECP) to a standard immunosuppressive drug therapy after heart transplantation in clinical studies has shown to be beneficial, for example, by reducing acute rejection, allograft vasculopathy or CMV infection. However, the protocols varied considerably, have a predetermined finite number of ECP treatments and adjuvant immunosuppressive regimens used in combination with ECP have differed significantly. Furthermore, there are scarce data to guide which patients should be treated with ECP and when or who would benefit further if ECP were to be continued long term to increase the safety by reducing immunosuppressive drug toxicities without losing efficacy. The knowledge of the tolerance-inducing effects of ECP-like upregulation of regulatory T cells and of dendritic cells may allow to develop a strategy to monitor immunomodulation effects of ECP to further identify ECP responders, the optimal individual ECP schedule and whether ECP therapy can replace or reduce immunosuppressive drug therapy.

T-cell energy metabolism as a controller of cell fate in transplantation

PURPOSE OF REVIEW

To highlight some of the recent developments in the novel field of immunometabolism and the therapeutic potential of the many regulatory components of this immunometabolic network for transplantation.

RECENT FINDINGS

In response to cytokines, changes in nutrients, and other alterations in the local milieu, immune cells are capable of changing their internal metabolic pathways to meet their energy demands. Recent studies demonstrate that activated T effectors (Th1 and Th17) are supported by aerobic glycolysis, whereas regulatory T cells and CD8 memory T cells favor fatty acid oxidation and lipid biosynthesis through mitochondrial oxidative phosphorylation. These bioenergetic processes are dependent upon the activation of metabolic sensors such as mammalian target of rapamycin and AMP-activated protein kinase, respectively, indicating that the cross-talk between immunity and metabolism can shape the fate and function of immune cells. Finally, exciting new studies suggest that differences in the bioenergetic mechanisms within the various immune subsets may selectively be exploited for regulating the immune responses.

SUMMARY

In this review, we will discuss the metabolic signatures adopted by various immune cells during tolerance versus immunity and the promising avenues that can be modulated by targeting metabolic pathways with either nutrition or pharmacological intervention for establishing long-term transplantation tolerance.

Abnormal quantity and function of regulatory T cells in peripheral blood of patients with severe aplastic anemia

Severe aplastic anemia is a rare autoimmune disease characterized by severe pancytopenia and bone marrow failure, which is caused by activated T lymphocytes. Tregs are believed to control development and progression of autoimmunity by suppressing autoreactive T cells. This study aims at understanding the quantity and function of peripheral Tregs in SAA. The expression of related biomarkers on Treg cell surface were determined by flow cytometry. The frequency of Tregs and the expression of CTLA-4 in SAA was significantly decreased than that in normal controls. The expression of perforin in SAA was significantly increased than that in controls, while expression of CD39, CD73 and GITR in Tregs did not show any significant difference between the two groups. These data revealed that CTLA-4 could be responsible for Treg abnormalities in SAA, but suppression mediated by perforin, CD39, CD73 and GITR, and survival capability of single Treg cell may not be injured.

Alloreactive regulatory T cells generated with retinoic acid prevent skin allograft rejection

CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells mediate immunological self-tolerance and suppress immune responses. Retinoic acid (RA), a natural metabolite of vitamin A, has been reported to enhance the differentiation of Treg cells in the presence of TGF-β. In this study, we show that the co-culture of naive T cells from C57BL/6 mice with allogeneic antigen-presenting cells (APCs) from BALB/c mice in the presence of TGF-β, RA, and IL-2 resulted in a striking enrichment of Foxp3(+) T cells. These RA in vitro-induced regulatory T (RA-iTreg) cells did not secrete Th1-, Th2-, or Th17-related cytokines, showed a nonbiased homing potential, and expressed several cell surface molecules related to Treg-cell suppressive potential. Accordingly, these RA-iTreg cells suppressed T-cell proliferation and inhibited cytokine production by T cells in in vitro assays. Moreover, following adoptive transfer, RA-iTreg cells maintained Foxp3 expression and their suppressive capacity. Finally, RA-iTreg cells showed alloantigen-specific immunosuppressive capacity in a skin allograft model in immunodeficient mice. Altogether, these data indicate that functional and stable allogeneic-specific Treg cells may be generated using TGF-β, RA, and IL-2. Thus, RA-iTreg cells may have a potential use in the development of more effective cellular therapies in clinical transplantation.

Immunological monitoring of extracorporeal photopheresis after heart transplantation

Extracorporeal photopheresis (ECP) has been used as a prophylactic and therapeutic option to avoid and treat rejection after heart transplantation (HTx). Tolerance-inducing effects of ECP such as up-regulation of regulatory T cells (T(regs)) are known, but specific effects of ECP on regulatory T cell (T(reg)) subsets and dendritic cells (DCs) are lacking. We analysed different subsets of T(regs) and DCs as well as the immune balance status during ECP treatment after HTx. Blood samples were collected from HTx patients treated with ECP for prophylaxis (n = 9) or from patients with histologically proven acute cellular rejection (ACR) of grade ≥ 1B (n = 9), as well as from control HTx patients without ECP (HTxC; n = 7). Subsets of T(regs) and DCs as well as different cytokine levels were analysed. Almost 80% of the HTx patients showed an effect to ECP treatment with an increase of T(regs) and plasmacytoid DCs (pDCs). The percentage of pDCs before ECP treatment was significantly higher in patients with no ECP effect (26·3% ± 5·6%) compared to patients who showed an effect to ECP (9·8% ± 10·2%; P = 0·011). Analysis of functional subsets of CD4⁺CD25(high)CD127(low) T(regs) showed that CD62L-, CD120b- and CD147-positive T(regs) did not differ between the groups. CD39-positive T(regs) increased during ECP treatment compared to HTxC. ECP-treated patients showed higher levels for T helper type 1 (Th1), Th2 and Th17 cytokines. Cytokine levels were higher in HTx patients with rejection before ECP treatment compared to patients with prophylactic ECP treatment. We recommend a monitoring strategy that includes the quantification and analysis of T(regs), pDCs and the immune balance status before and up to 12 months after starting ECP.

Surface antigen profiles of leukocytes and melanoma cells in lymph node metastases are associated with survival in AJCC stage III melanoma patients

There is an urgent need to identify more accurate prognostic biomarkers in melanoma patients, particularly in those with metastatic disease. This study aimed to identify melanoma and leukocyte surface antigens predictive of survival in a prospective series of AJCC stage IIIb/c melanoma patients (n = 29). Live cell suspensions were prepared from melanoma metastases within lymph nodes (LN). The suspensions were immuno-magnetically separated into CD45⁺ (leukocyte) and CD45⁻ (non-hematopoietic, enriched melanoma cell) fractions. Surface antigens on CD45⁻ and CD45⁺ cell populations were profiled using DotScan™ microarrays (Medsaic Pty. Ltd.) and showed differential abundance levels for 52 and 78 antigens respectively. Associations of the surface profiles with clinicopathologic and outcome data (median follow-up 35.4 months post LN resection) were sought using univariate (log-rank test) and multivariate (Wald’s test; modelled with patient’s age, gender and AJCC staging at LN recurrence) survival models. CD9 (p = 0.036), CD39 (p = 0.004) and CD55 (p = 0.005) on CD45⁺ leukocytes were independently associated with distant metastasis-free survival using multivariate analysis. Leukocytes with high CD39 levels were also significantly associated with increased overall survival (OS) in multivariate analysis (p = 0.016). LNs containing leukocytes expressing CD11b (p = 0.025), CD49d (p = 0.043) and CD79b (p = 0.044) were associated with reduced OS on univariate analysis. For enriched melanoma cells (CD45⁻ cell populations), 11 surface antigens were significantly correlated with the disease-free interval (DFI) between diagnosis of culprit primary melanoma and LN metastasis resection. Nine antigens on CD45⁺ leukocytes also correlated with DFI. Following validation in independent datasets, surface markers identified here should enable more accurate determination of prognosis in stage III melanoma patients and provide better risk stratification of patients entering clinical trials.

Graft-versus-host disease is enhanced by selective CD73 blockade in mice

CD73 functions as an ecto-5′-nucleotidase to produce extracellular adenosine that has anti-inflammatory and immunosuppressive activity. We here demonstrate that CD73 helps control graft-versus-host disease (GVHD) in mouse models. Survival of wild-type (WT) recipients of either allogeneic donor naïve CD73 knock-out (KO) or WT T cells was similar suggesting that donor naïve T cell CD73 did not contribute to GVHD. By contrast, donor CD73 KO CD4⁺CD25⁺ regulatory T cells (Treg) had significantly impaired ability to mitigate GVHD mortality compared to WT Treg, suggesting that CD73 on Treg is critical for GVHD protection. However, compared to donor CD73, recipient CD73 is more effective in limiting GVHD. Pharmacological blockade of A2A receptor exacerbated GVHD in WT recipients, but not in CD73 KO recipients, suggesting that A2 receptor signaling is primarily implicated in CD73-mediated GVHD protection. Moreover, pharmacological blockade of CD73 enzymatic activity induced stronger alloreactive T cell activity, worsened GVHD and enhanced the graft-versus-leukemia (GVL) effect. These findings suggest that both donor and recipient CD73 protects against GVHD but also limits GVL effects. Thus, either enhancing or blocking CD73 activity has great potential clinical application in allogeneic bone marrow transplants.

Ectonucleotidases in solid organ and allogeneic hematopoietic cell transplantation

Extracellular nucleotides are ubiquitous signalling molecules which modulate distinct physiological and pathological processes. Nucleotide concentrations in the extracellular space are strictly regulated by cell surface enzymes, called ectonucleotidases, which hydrolyze nucleotides to the respective nucleosides. Recent studies suggest that ectonucleotidases play a significant role in inflammation by adjusting the balance between ATP, a widely distributed proinflammatory danger signal, and the anti-inflammatory mediator adenosine. There is increasing evidence for a central role of adenosine in alloantigen-mediated diseases such as solid organ graft rejection and acute graft-versus-host disease (GvHD). Solid organ and hematopoietic cell transplantation are established treatment modalities for a broad spectrum of benign and malignant diseases. Immunological complications based on the recognition of nonself-antigens between donor and recipient like transplant rejection and GvHD are still major challenges which limit the long-term success of transplantation. Studies in the past two decades indicate that purinergic signalling influences the severity of alloimmune responses. This paper focuses on the impact of ectonucleotidases, in particular, NTPDase1/CD39 and ecto-5'-nucleotidase/CD73, on allograft rejection, acute GvHD, and graft-versus-leukemia effect, and on possible clinical implications for the modulation of purinergic signalling after transplantation.

Are we ready for the use of foxp3(+) regulatory T cells for immunodiagnosis and immunotherapy in kidney transplantation?

The existence of T-cell subsets naturally committed to perform immunoregulation has led to enthusiastic efforts to investigate their role in the immunopathogenesis of transplantation. Being able to modulate alloresponses, regulatory T cells could be used as an immunodiagnostic tool in clinical kidney transplantation. Thus, the measurement of Foxp3 transcripts, the presence of regulatory T cells in kidney biopsies, and the phenotypic characterisation of the T-cell infiltrate could aid in the diagnosis of rejection and the immune monitoring and prediction of outcomes in kidney transplantation. Interestingly, the adoptive transfer of regulatory T cells in animal models has been proven to downmodulate powerful alloresponses, igniting translational research on their potential use as an immunomodulatory therapy. For busy transplant clinicians, the vast amount of information in the literature on regulatory T cells can be overwhelming. This paper aims to highlight the most applicable research findings on the use of regulatory T cells in the immune diagnosis and potential immunomodulatory therapy of kidney transplant patients. However, can we yet rely on differential regulatory T-cell profiles for the identification of rejection or to tailor patient's immunosuppression? Are we ready to administer regulatory T cells as inductive or adjunctive therapy for kidney transplantation?

Expression of CD39 on FoxP3+ T regulatory cells correlates with progression of HBV infection

Background

Although it is known that regulatory T cells (Tregs) can suppress the function of effector T cells, and may contribute to impaired immune response, the precise role of Tregs during the course of hepatitis B virus (HBV) infection remains to be elucidated. A newly identified subset of the CD4⁺Foxp3⁺ Tregs, the CD39⁺ Tregs, has been associated with viral infections and autoimmune diseases. Therefore, we hypothesized that this discrete Treg subset may contribute to the chronic infection of HBV.

Results

Initial characterization studies of healthy peripheral CD39⁺FoxP3⁺CD4⁺ T cells revealed that the majority were CD45RA^- Treg cells. Subsequent analysis of HBV-infected patients (38 asymptomatic HBV carriers (AsCs), 37 chronic active hepatitis B (CAH), 29 HBV-associated acute-on-chronic liver failure (ACLF)) and healthy individuals (25 controls) was conducted to assess association with HBV copy number and the liver injury marker alanine aminotransferase (ALT). A higher percentage of CD39⁺ Tregs was detected within the population of FoxP3⁺CD4⁺ T cells in peripheral blood of AsCs patients. Moreover, the percentage of CD39⁺ Tregs was significantly less in CAH and ACLF patients. The increased proportions of circulating CD39⁺ Tregs were positively correlated with serum viral load, but inversely correlated with serum ALT level.

Conclusion

These findings not only suggest that CD39⁺ Treg cells may be involved in HBV disease progression but also identify CD39⁺ Tregs as a dynamic immune regulatory cell population that may represent a new target of immunomodulatory therapeutic interventions.

Amelioration of acute graft-versus-host disease by adoptive transfer of ex vivo expanded human cord blood CD4+CD25+ forkhead box protein 3+ regulatory T cells is associated with the polarization of Treg/Th17 balance in a mouse model

BACKGROUND

Human cord blood (CB) is a superior source of regulatory T cells (Tregs) compared with peripheral blood. Initial studies have shown that CB-derived Tregs can be effectively expanded ex vivo. However, in vitro suppressor activity of expanded CB-Tregs and their efficacy in the prevention of acute graft-versus-host disease (aGVHD) in vivo are poorly understood.

STUDY DESIGN AND METHODS

In vitro, human CB CD4+CD25+ T cells expanded with anti-CD3/CD28 beads plus interleukin (IL)-2 and the phenotypes, expression of cytokines, and suppression of expanded cells were analyzed after two cycles of stimulation. In vivo, the addition of human CB-Tregs was transferred in the major histocompatibility complex-mismatched aGVHD mouse model. Survival, body weight, GVHD scoring, histopathologic specimens, serum cytokines, and Th subsets were analyzed in CB-Treg-treated mice and untreated controls.

RESULTS

After being expanded ex vivo, human CB-derived Tregs with potent suppressor function could meet clinical demands. Up to 85% of mice with CB-Tregs treatment survived beyond Day 63 after bone marrow transplantation; however, all aGVHD mice died within 18 days. In the serum of the CB-Treg-treated mice, the production of transforming growth factor-β increased continuously, as opposed to IL-17, which decreased quickly. Consistent with the changes of cytokines, the percentage of mouse CD4+ forkhead box protein 3+ Tregs increased while that of Th17 cells decreased.

CONCLUSION

Ex vivo expanded human CB-Tregs significantly prevented allogeneic aGVHD in vivo by modulating various cytokine secretion and polarizing the Treg/Th17 balance toward Treg, which suggests the potential use of expanded CB-Tregs as a therapeutic approach for GVHD.

Distinct regulatory CD4+T cell subsets; differences between naïve and antigen specific T regulatory cells

Effector T cells have functional subpopulations with distinct cytokine, cytokine receptor, chemokine receptor and transcription factors. We review how activation of antigen specific Treg induces expression of cytokines, cytokine receptors and chemokine receptors depending upon the effector lineage they are activated by. Activated Treg express receptors that are directly related to the effector T cell lineage. Other classes of Treg are induced in the periphery from effector lineage CD4(+)CD25(-)FOXP3(-)CD127(high)T cells, either by IL-10 or TGF-β or by association with activated CD4(+)CD25(+)FOXP3(+)Treg. Thus Treg are produced and adapt to the specific immune inflammatory environment they are activated within. Activated Treg produce different molecules to mediate suppression, which are tailored to the immune response they are activated by and control.

Multipotent mesenchymal stromal cells express FoxP3: a marker for the immunosuppressive capacity?

Multipotent mesenchymal stromal cells (MSCs) have immunosuppressive capacity but the exact mechanism by which they suppress proliferation of T lymphocytes is not fully understood. Recently, the characteristics and function of regulatory T lymphocytes (Tregs) have become better defined. Tregs and MSCs have immunosuppressive features in common. Here, we looked for a common basis for immunosuppression in these distinct cell types. Forkhead box P3 (FoxP3) and CD39 expression in MSCs was measured by flow cytometry and real-time quantitative polymerase chain reaction. The importance of FoxP3 in MSC-mediated immunosuppression was investigated by siRNA technology and mixed lymphocyte culture (MLC). The effect of 5-azacytidine and other immunosuppressive drugs on FoxP3 expression and immunosuppression by MSCs was explored by flow cytometry, MLC, and real-time quantitative polymerase chain reaction. MSCs express FoxP3 at variable levels, but they do not express CD39. FoxP3 MSCs suppress MLC to a greater extent than cells with lower FoxP3 expression. However, FoxP3-decreased MSCs were found to retain their immunosuppressive properties. 5-azacytitine had no effect on FoxP3 expression or MLC suppression by MSCs. However, immunosuppressive drugs led to increased FoxP3 levels and MLC inhibition in FoxP3 MSCs. This is the first demonstration of FoxP3 expression by MSCs. Although MSCs share several features with Tregs, and FoxP3 MSCs tend to be more immunosuppressive, MSCs do not require functional FoxP3 for their immunosuppressive activity. The increased MSC-mediated suppression of immune responses by immunosuppressive drugs deserves further investigation.

Adenosine A2(A) receptor modulates the oxidative stress response of primed polymorphonuclear leukocytes after parabolic flight

Space flight and gravitational stress can alter innate immune function. Parabolic flights (PFs) as a model for short-term gravitational changes prime the cytotoxic capability of polymorphonuclear leukocytes (PMNs). In view of the emerging role of adenosine in the regulation of innate immune responses, we examined the potency of adenosine to control the release of cytotoxic H(2)O(2) by primed PMNs via the adenosine receptor system. During PFs, microgravity conditions (<10(-2) G) are generated for approximately 22 seconds, followed by a hypergravity (1.8 G) phase resulting in gravitational stress. We studied the ex vivo effects of adenosine on the production of H(2)O(2) by stimulated PMNs and determined adenosine plasma levels and adenosine A2(A) receptor transcripts of leukocytes of PF participants (n = 15). Increasing concentrations of adenosine dose dependently reduced tissue-toxic H(2)O(2) production by PMNs with a half-maximal inhibitory concentration (IC(50)) of 19.5 nM before takeoff and 7.6 nM at 48 hours after PF. This increase in the adenosine-mediated inhibition of PMNs' H(2)O(2) production was completely reversed by addition of the A2(A) receptor antagonist ZM241385. PF induced a nonsignificant elevation in adenosine plasma levels; A2(A) receptor mRNA from leukocytes remained almost unchanged. Adenosine limits the oxidative stress response of PMNs after PFs through an upregulation of the adenosine A2(A) receptor function. This stop signal on inflammation is stronger than that under normal physiologic states and may limit further cytotoxic damage. Pharmacologic manipulation of the adenosine A2(A) receptor pathway could be a potential target for control of unwanted exacerbations of cytotoxic PMN functions.