Dependence of immunoglobulin class switch recombination in B cells on vesicular release of ATP and CD73 ectonucleotidase activity. Cell Rep. 2013;3:1824-1831. [PMID: 23770243 DOI: 10.1016/j.celrep.2013.05.022]

Tissue-specific sex differences in pediatric and adult immune cell composition and function

Sex-based differences in immune cell composition and function can contribute to distinct adaptive immune responses. Prior work has quantified these differences in peripheral blood, but little is known about sex differences within human lymphoid tissues. Here, we characterized the composition and phenotypes of adaptive immune cells from male and female ex vivo tonsils and evaluated their responses to influenza antigens using an immune organoid approach. In a pediatric cohort, female tonsils had more memory B cells compared to male tonsils direct ex vivo and after stimulation with live-attenuated but not inactivated vaccine, produced higher influenza-specific antibody responses. Sex biases were also observed in adult tonsils but were different from those measured in children. Analysis of peripheral blood immune cells from in vivo vaccinated adults also showed higher frequencies of tissue homing CD4 T cells in female participants. Together, our data demonstrate that distinct memory B and T cell profiles are present in male vs. female lymphoid tissues and peripheral blood respectively and suggest that these differences may in part explain sex biases in response to vaccines and viruses.

Oxidative phosphorylation regulates B cell effector cytokines and promotes inflammation in multiple sclerosis

Dysregulated B cell cytokine production contributes to pathogenesis of immune-mediated diseases including multiple sclerosis (MS); however, the underlying mechanisms are poorly understood. In this study we investigated how cytokine secretion by pro-inflammatory (GM-CSF-expressing) and anti-inflammatory (IL-10-expressing) B cells is regulated. Pro-inflammatory human B cells required increased oxidative phosphorylation (OXPHOS) compared with anti-inflammatory B cells. OXPHOS reciprocally modulated pro- and anti-inflammatory B cell cytokines through regulation of adenosine triphosphate (ATP) signaling. Partial inhibition of OXPHOS or ATP-signaling including with BTK inhibition resulted in an anti-inflammatory B cell cytokine shift, reversed the B cell cytokine imbalance in patients with MS, and ameliorated neuroinflammation in a myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalitis mouse model. Our study identifies how pro- and anti-inflammatory cytokines are metabolically regulated in B cells and identifies ATP and its metabolites as a "fourth signal" that shapes B cell responses and is a potential target for restoring the B cell cytokine balance in autoimmune diseases.

Calcium homeostasis modulator 2 (Calhm2) as slowly activating membrane current channel in mouse B cells

In mouse B lymphocytes, an unidentified slow-activating voltage-dependent current resembling the characteristics of the Calhm family ion channel (ICalhm-L) was investigated. RT-PCR analysis revealed the presence of Calhm2 and 6 transcripts, with subsequent whole-cell patch-clamp studies indicating that the ICalhm-L is augmented by heat, alkaline pH, and low extracellular [Ca2+]. Overexpression of Calhm2, but not Calhm6, in N2A cells recapitulated ICalhm-L. Moreover, Calhm2 knockdown in Bal-17 cells abolished ICalhm-L. We firstly identify the voltage-dependent ion channel function of the Calhm2 in the mouse immune cells. ATP release assays in primary mouse B cells suggested a significant contribution of Calhm2 for purinergic signaling at physiological temperature.

CD39 expression on immune cells predicts methotrexate response in rheumatoid arthritis patients

Background/aim

Rheumatoid arthritis (RA) is a chronic inflammatory disease affecting mostly small joints, such as hand and foot joints symmetrically with irreversible joint destruction. In this study, the relationship between CD39 expression and the treatment response of RA patients was examined to investigate its potential as a biomarker that demonstrates treatment response.

Materials and methods

This study included 77 RA patients and 40 healthy controls (HC). The RA patients were divided into 2 groups based on their response to RA treatment, those with a good response to methotrexate (MTX) monotherapy and those with an inadequate response based on the American College of Rheumatology and the European League Against Rheumatism response criteria. Various immunological parameters and Disease Activity Score in 28 Joints (DAS28) were examined between the groups using the Student's t-test.

Results

The monocytic myeloid-derived suppressor cell (M-MDSC) percentage was higher in the RA patient group versus the HC group. The CD39 expression in the T lymphocytes were higher in patients that responded well to the MTX compared to those showing inadequate response. Additionally, s negative correlation was found between the DAS28 and CD39 in the T cells.

Conclusion

The results showed that the improvement in treatment response to the therapy in RA patients could be because of the enhancement in the CD39/adenosine (ADO) pathway. Therefore, therapies targeting the CD39/ADO pathway in T cells may improve RA treatments.

Deficiency of adenosine deaminase 2 (DADA2): Review

The deficiency of adenosine deaminase 2 (DADA2) is an autosomal recessive disease caused by loss-of-function (LOF) mutations in the ADA2 gene and was first described in 2014. Initially, it was described as vasculopathy/vasculitis that mostly affected infants and young children and closely resembled polyarteritis nodosa (PAN). Skin rash and ischemic/hemorrhagic stroke are predominant symptoms. However, the clinical spectrum of DADA2 has continued to expand since then. It has now been reported in adults as well. Besides vasculitis-related manifestations, hematological, immunological, and autoinflammatory manifestations are now well recognized. More than 100 disease-causing mutations have been described. The decrease in ADA2 enzyme leads to an increased extracellular adenosine level that, in turn, triggers a proinflammatory cascade. The disease is highly variable, and patients carrying same mutation may have different ages of presentation and clinical features. Anti-tumor necrosis factor (TNF) agents are mainstay of treatment of the vasculitis/vasculopathy phenotype. Hematopoietic stem cell transplant (HSCT) has been performed in patients with severe hematological manifestations. Recombinant ADA2 protein and gene therapy hold a promise for future.

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.

Anti-CD73 antibody activates human B cells, enhances humoral responses and induces redistribution of B cells in patients with cancer

BACKGROUND

CD73 is widely expressed on immune cells playing a critical role in immunomodulatory functions including cell adhesion and migration, as a costimulatory molecule for T cells and in production of adenosine. The function of CD73 expressed on B cells has not been fully characterized. Mupadolimab is an anti-human CD73 antibody that activates B cells. We evaluated the characteristics of this antibody and its effects on immune cells in vitro and in vivo.

METHODS

Mupadolimab binding to CD73, inhibition of CD73 enzymatic activity, and effects on lymphocyte activation were evaluated in vitro by measuring changes in immunophenotype by flow cytometry. Cryogenic-transmission electron microscopy was used to determine epitope binding. Effects on human B cells in vivo were evaluated in immunodeficient NSG-SGM3 mice immunized with SARS-CoV-2 and influenza viral antigens. Safety and immune effects were evaluated in the completed dose escalation portion of a phase 1 trial conducted in patients with cancer.

RESULTS

Mupadolimab binds to a unique epitope on CD73^POS B cells resulting in their activation and differentiation through B cell receptor signaling pathways. Mupadolimab induces expression of CD69, CD83, CD86 and MHC class II on B cells along with morphological transformation into plasmablasts and expression of CD27, CD38 and CD138. These effects are independent of adenosine. Mupadolimab binds to the N-terminal of CD73 in the closed position and competitively inhibits substrate binding. Mupadolimab enhanced antigen specific antibody response to SARS-CoV-2 spike protein and influenza hemagglutinin in humanized mouse models. Mupadolimab was evaluated as a monotherapy in a phase 1 trial (NCT03454451) in 34 patients with advanced cancer and demonstrated binding to CD73^POS circulating cells and transient reduction in the number of B cells, with return of CD73^NEG B cells with memory phenotype. No dose-limiting toxicities or changes in serum immunoglobulins were seen.

CONCLUSIONS

Mupadolimab activates B cells and stimulates the production of antigen specific antibodies. The effects in patients with cancer suggest that activated, CD69^POS B cells redistribute to lymphoid tissues. Minor tumor regression was observed in several patients. These results support further investigation of mupadolimab as an immunotherapy for cancer and its potential use as a vaccine adjuvant.

TRIAL REGISTRATION NUMBER

NCT03454451.

IgM+ and IgM- memory B cells represent heterogeneous populations capable of producing class-switched antibodies and germinal center B cells upon rechallenge with P. yoelii

Memory B cells (MBCs) are essential for maintaining long-term humoral immunity to infectious organisms, including Plasmodium. MBCs are a heterogeneous population whose function can be dictated by isotype or expression of particular surface proteins. Here, aided by antigen-specific B-cell tetramers, MBC populations were evaluated to discern their phenotype and function in response to infection with a nonlethal strain of P. yoelii. Infection of mice with P. yoelii 17X resulted in 2 predominant MBC populations: somatically hypermutated isotype-switched (IgM- ) and IgM+ MBCs that coexpressed CD73 and CD80 that produced antigen-specific antibodies in response to secondary infection. Rechallenge experiments indicated that IgG-producing cells dominated the recall response over the induction of IgM-secreting cells, with both populations expanding with similar timing during the secondary response. Furthermore, using ZsGreen1 expression as a surrogate for activation-induced cytidine deaminase expression alongside CD73 and CD80 coexpression, ZsGreen1+ CD73+ CD80+ IgM+ , and IgM- MBCs gave rise to plasmablasts that secreted Ag-specific Abs after adoptive transfer and infection with P. yoelii. Moreover, ZsGreen1+ CD73+ CD80+ IgM+ and IgM- MBCs could differentiate into B cells with a germinal center phenotype after adoptive transfer. A third population of B cells (ZsGreen1- CD73- CD80- IgM- ) that is apparent after infection responded poorly to reactivation in vitro and in vivo, indicating that these cells do not represent a canonical population of MBCs. Together these data indicated that MBC function is not defined by immunoglobulin isotype, nor does coexpression of key surface markers limit the potential fate of MBCs after recall.

Dysfunctional purinergic signaling correlates with disease severity in COVID-19 patients

Ectonucleotidases modulate inflammatory responses by balancing extracellular ATP and adenosine (ADO) and might be involved in COVID-19 immunopathogenesis. Here, we explored the contribution of extracellular nucleotide metabolism to COVID-19 severity in mild and severe cases of the disease. We verified that the gene expression of ectonucleotidases is reduced in the whole blood of patients with COVID-19 and is negatively correlated to levels of CRP, an inflammatory marker of disease severity. In line with these findings, COVID-19 patients present higher ATP levels in plasma and reduced levels of ADO when compared to healthy controls. Cell type-specific analysis revealed higher frequencies of CD39+ T cells in severely ill patients, while CD4+ and CD8+ expressing CD73 are reduced in this same group. The frequency of B cells CD39+CD73+ is also decreased during acute COVID-19. Interestingly, B cells from COVID-19 patients showed a reduced capacity to hydrolyze ATP into ADP and ADO. Furthermore, impaired expression of ADO receptors and a compromised activation of its signaling pathway is observed in COVID-19 patients. The presence of ADO in vitro, however, suppressed inflammatory responses triggered in patients’ cells. In summary, our findings support the idea that alterations in the metabolism of extracellular purines contribute to immune dysregulation during COVID-19, possibly favoring disease severity, and suggest that ADO may be a therapeutic approach for the disease.

Lack of Ecto-5′-Nucleotidase Protects Sensitized Mice against Allergen Challenge

Ecto-5′-nucleotidase (CD73), the ectoenzyme that together with CD39 is responsible for extracellular ATP hydrolysis and adenosine accumulation, regulates immune/inflammatory processes by controlling innate and acquired immunity cell functions. We previously demonstrated that CD73 is required for the assessment of a controlled allergic sensitization, in mice. Here, we evaluated the response to aerosolized allergen of female-sensitized mice lacking CD73 in comparison with their wild type counterpart. Results obtained show, in mice lacking CD73, the absence of airway hyperreactivity in response to an allergen challenge, paralleled by reduced airway CD23⁺B cells and IL4⁺T cells pulmonary accumulation together with reduced mast cells accumulation and degranulation. Our findings indicate CD73 as a potential therapeutic target for allergic asthma.

Type I interferon activation in RAS-associated autoimmune leukoproliferative disease (RALD)

RAS-associated autoimmune leukoproliferative disease (RALD) is a rare immune dysregulation syndrome caused by somatic gain-of-function mutations of either NRAS or KRAS gene in hematopoietic cells. We describe a 27-year-old patient presenting at 5 months of age with recurrent infections and generalized lymphadenopathy who developed a complex multi-organ autoimmune syndrome with hypogammaglobulinemia, partially controlled with oral steroids, hydroxichloroquine, mofetil mycophenolate and IVIG prophylaxis. Activation of type I interferon pathway was observed in peripheral blood. Since 18 years of age, the patient developed regenerative nodular hyperplasia of the liver evolving into hepatopulmonary syndrome. Whole exome sequencing analysis of the peripheral blood DNA showed the NRAS p.Gly13Asp mutation validated as somatic. Our report highlights the possibility of detecting somatic NRAS gene mutations in patients with inflammatory immune dysregulation and type I interferon activation.

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.

Profiling B cell immunodominance after SARS-CoV-2 infection reveals antibody evolution to non-neutralizing viral targets

Dissecting the evolution of memory B cells (MBCs) against SARS-CoV-2 is critical for understanding antibody recall upon secondary exposure. Here, we used single-cell sequencing to profile SARS-CoV-2-reactive B cells in 38 COVID-19 patients. Using oligo-tagged antigen baits, we isolated B cells specific to the SARS-CoV-2 spike, nucleoprotein (NP), open reading frame 8 (ORF8), and endemic human coronavirus (HCoV) spike proteins. SARS-CoV-2 spike-specific cells were enriched in the memory compartment of acutely infected and convalescent patients several months post symptom onset. With severe acute infection, substantial populations of endemic HCoV-reactive antibody-secreting cells were identified and possessed highly mutated variable genes, signifying preexisting immunity. Finally, MBCs exhibited pronounced maturation to NP and ORF8 over time, especially in older patients. Monoclonal antibodies against these targets were non-neutralizing and non-protective in vivo. These findings reveal antibody adaptation to non-neutralizing intracellular antigens during infection, emphasizing the importance of vaccination for inducing neutralizing spike-specific MBCs.

Heterogeneity of meningeal B cells reveals a lymphopoietic niche at the CNS borders

The meninges contain adaptive immune cells that provide immunosurveillance of the central nervous system (CNS). These cells are thought to derive from the systemic circulation. Through single-cell analyses, confocal imaging, bone marrow chimeras, and parabiosis experiments, we show that meningeal B cells derive locally from the calvaria, which harbors a bone marrow niche for hematopoiesis. B cells reach the meninges from the calvaria through specialized vascular connections. This calvarial-meningeal path of B cell development may provide the CNS with a constant supply of B cells educated by CNS antigens. Conversely, we show that a subset of antigen-experienced B cells that populate the meninges in aging mice are blood-borne. These results identify a private source for meningeal B cells, which may help maintain immune privilege within the CNS.

The CD39+ HBV surface protein-targeted CAR-T and personalized tumor-reactive CD8+ T cells exhibit potent anti-HCC activity

CD39, expressed by tumor-infiltrating lymphocytes (TILs), is a marker to identify tumor-reactive T cells, which is frequently associated with stronger antitumor activity than bystander T cells in a variety of malignancies. Therefore, CD39 could be a promising marker for identifying the active antitumor immune cells used for cellular immunotherapy. To test this possibility, we constructed the hepatitis B virus (HBV) surface protein-specific chimeric antigen receptor T cells (HBVs-CAR-T cells) and generated the personalized tumor-reactive CD8⁺ T cells. We subsequently assessed their antitumor efficiency mainly with a co-culture system for autologous HBVs⁺ HCC organoid and T cells. We found that both CD39⁺ HBVs-CAR-T and CD39⁺ personalized tumor-reactive CD8⁺ T cells induced much more apoptosis in HCC organoids. Although the exhaustion status of CAR-T cells increased in CD39⁺ CAR-T cells, triple knockdown of PD-1, Tim-3, and Lag-3 with shRNAs further enhanced antitumor activity in CD39⁺ CAR-T cells. Furthermore, these CD39⁺ CAR-T cells exerted an increased secretion of interferon-γ and stronger antitumor effect in a patient-derived xenograft mouse model. Our findings demonstrated that CD39 could be a promising biomarker to enrich active immune cells and become an indicator marker for evaluating the prognosis of immunotherapy for HCC patients.

Expanding spectrum of DADA2: a review of phenotypes, genetics, pathogenesis and treatment

Deficiency of adenosine deaminase 2 (DADA2) is a monogenic disease caused by biallelic mutations in ADA2 gene (previously CECR1). The aim of this review was to describe the clinical phenotypes, genetics, pathogenesis and treatment of DADA2. ADA2 is highly expressed on myeloid cells and deficiency leads to polarisation of macrophages to an M1 inflammatory type and activation of neutrophils. The pathogenesis of immunological and haematological manifestations is less clear. The spectrum of clinical presentations varies widely from asymptomatic individual to severe vasculitis, several autoinflammatory, immunological and haematological manifestations. Initially considered a childhood disease, the first presentation is now being reported well into adulthood. Vasculitis closely resembles polyarteritis nodosa. Livedoid reticularis/racemosa like skin rash and central nervous system involvement in the form of ischemic or haemorrhagic stroke are dominant manifestations. Immunological manifestations include hypogammaglobulinemia and recurrent infections. Lymphopenia is the most common haematological manifestation; pure red cell aplasia and bone marrow failure has been reported in severe cases. The disease is extremely heterogeneous with variable severity noted in patients with the same mutation and even within family members. Tumour necrosis factor inhibitors are currently the treatment of choice for vasculitic and inflammatory manifestations and also prevent strokes. Haematopoietic stem cell transplantation is a curative option for severe haematological manifestations like pure red cell aplasia, bone marrow failure and immunodeficiency. Further research is required to understand pathogenesis and all clinical aspects of this disease to enable early diagnosis and prompt treatment. Key Points • Deficiency of adenosine deaminase 2 (DADA2) is a monogenic disease caused by biallelic mutations in ADA2 gene. • The clinical features include vasculitis resembling polyarteritis nodosa, autoinflammation, haematological manifestations and immunodeficiency. • The severity varies widely from mild to fatal even in patients within a family and with the same mutation. • The treatment of choice for inflammatory and vasculitic disease is tumour necrosis factor α blockers. Bone marrow transplant may be considered for severe haematological disease.

Ectonucleotidases in Acute and Chronic Inflammation

Ectonucleotidases are extracellular enzymes with a pivotal role in inflammation that hydrolyse extracellular purine and pyrimidine nucleotides, e.g., ATP, UTP, ADP, UDP, AMP and NAD⁺. Ectonucleotidases, expressed by virtually all cell types, immune cells included, either as plasma membrane-associated or secreted enzymes, are classified into four main families: 1) nucleoside triphosphate diphosphohydrolases (NTPDases), 2) nicotinamide adenine dinucleotide glycohydrolase (NAD glycohydrolase/ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase 1), 3) ecto-5′-nucleotidase (NT5E), and 4) ecto-nucleotide pyrophosphatase/phosphodiesterases (NPPs). Concentration of ATP, UTP and NAD⁺ can be increased in the extracellular space thanks to un-regulated, e.g., cell damage or cell death, or regulated processes. Regulated processes include secretory exocytosis, connexin or pannexin hemichannels, ATP binding cassette (ABC) transporters, calcium homeostasis modulator (CALMH) channels, the ATP-gated P2X7 receptor, maxi-anion channels (MACs) and volume regulated ion channels (VRACs). Hydrolysis of extracellular purine nucleotides generates adenosine, an important immunosuppressant. Extracellular nucleotides and nucleosides initiate or dampen inflammation via P2 and P1 receptors, respectively. All these agents, depending on their level of expression or activation and on the agonist concentration, are potent modulators of inflammation and key promoters of host defences, immune cells activation, pathogen clearance, tissue repair and regeneration. Thus, their knowledge is of great importance for a full understanding of the pathophysiology of acute and chronic inflammatory diseases. A selection of these pathologies will be briefly discussed here.

Understanding Early-Life Adaptive Immunity to Guide Interventions for Pediatric Health

Infants are capable of mounting adaptive immune responses, but their ability to develop long-lasting immunity is limited. Understanding the particularities of the neonatal adaptive immune system is therefore critical to guide the design of immune-based interventions, including vaccines, in early life. In this review, we present a thorough summary of T cell, B cell, and humoral immunity in early life and discuss infant adaptive immune responses to pathogens and vaccines. We focus on the differences between T and B cell responses in early life and adulthood, which hinder the generation of long-lasting adaptive immune responses in infancy. We discuss how knowledge of early life adaptive immunity can be applied when developing vaccine strategies for this unique period of immune development. In particular, we emphasize the use of novel vaccine adjuvants and optimization of infant vaccine schedules. We also propose integrating maternal and infant immunization strategies to ensure optimal neonatal protection through passive maternal antibody transfer while avoiding hindering infant vaccine responses. Our review highlights that the infant adaptive immune system is functionally distinct and uniquely regulated compared to later life and that these particularities should be considered when designing interventions to promote pediatric health.

B cell analysis in SARS-CoV-2 versus malaria: Increased frequencies of plasmablasts and atypical memory B cells in COVID-19

B cells play a central role in antiviral and antiparasitic immunity, not only as producers of antibodies, but also as APCs and mediators of inflammation. In this study, we used 16-color flow cytometry analysis to investigate the frequency, differentiation, and activation status of peripheral B cells of patients with SARS-CoV-2 infection or acute Plasmodium falciparum malaria compared with the healthy individuals. As a main result, we observed an increase of the frequency of (CD27^-, CD21^-) atypical memory B cells and (CD19⁺, CD27⁺, CD38⁺) plasmablasts in malaria and COVID-19 patients. Additionally, CD86, PD-1, CXCR3, and CD39 expression was up-regulated, whereas CD73 was down-regulated on plasmablasts of COVID-19 and malaria patients compared with the bulk B cell population. In particular, there was a more pronounced loss of CD73⁺ B cells in malaria. The frequency of plasmablasts positively correlated with serum levels of CRP, IL-6, and LDH of COVID-19 patients. In the longitudinal course of COVID-19, a rapid normalization of the frequency of atypical memory B cells was observed. The role and function of plasmablasts and atypical memory B cells in COVID-19 and other acute infections remain to be further investigated. The role of B cells as either "driver or passenger" of hyperinflammation during COVID-19 needs to be clarified.

B cells from Patients with Rheumatoid Arthritis Show Conserved CD39-Mediated Regulatory Function and increased CD39 Expression After Positive Response to Therapy

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by progressive joint destruction associated with increased pro-inflammatory mediators. In inflammatory microenvironments, exogenous ATP (eATP) is hydrolyzed to adenosine, which exerts immunosuppressive effects, by the consecutive action of the ectonucleotidases CD39 and CD73. Mature B cells constitutively express both ectonucleotidases, converting these cells to potential suppressors. Here, we assessed CD39 and CD73 expression on B cells from treated or untreated patients with RA. Neither the frequency of CD73⁺CD39⁺ and CD73^-CD39⁺ B cell subsets nor the levels of CD73 and CD39 expression on B cells from untreated or treated RA patients showed significant changes in comparison to healthy controls (HC). CpG+IL-2-stimulated B cells from HC or untreated RA patients increased their CD39 expression, and suppressed CD4⁺ and CD8⁺ T cell proliferation and intracellular TNF-production. A CD39 inhibitor significantly restored proliferation and TNF-producing capacity in CD4⁺ T cells, but not in CD8⁺ T cells, from HC and untreated RA patients, indicating that B cells from untreated RA patients conserved CD39-mediated regulatory function. Good responder patients to therapy (R-RA) exhibited an increased CD39 but not CD73 expression on B cells after treatment, while most of the non-responder (NR) patients showed a reduction in ectoenzyme expression. The positive changes of CD39 expression on B cells exhibited a negative correlation with disease activity and rheumatoid factor levels. Our results suggest modulating the ectoenzymes/ADO pathway as a potential therapy target for improving the course of RA.

Skewed CD39/CD73/adenosine pathway contributes to B-cell hyperactivation and disease progression in patients with chronic hepatitis B

Background

The mechanisms underlying B-cell hyperactivation in patients with chronic hepatitis B virus (HBV) infection remain largely undefined. The present study assessed the clinical characteristics of the CD39/CD73/adenosine pathway in patients with chronic hepatitis B (CHB).

Methods

We examined CD39 and CD73 expression and adenosine production by B-cells from 202 HBV-infected patients. B-cell-activation phenotypes were assessed by flow cytometry after CpG+CD40 ligand stimulation with or without blockade and activation of the adenosine pathway.

Results

CD39 and CD73 expression on circulating B-cells was decreased in CHB patients with high HBV DNA, HBeAg positivity, high HBsAg levels, and active liver inflammation, and was hierarchically restored in complete responders according to HBeAg seroconversion or HBsAg reduction. However, CD39 and CD73 expression on activated memory and tissue-like memory B-cell subsets in complete responders was not increased despite effective antiviral treatments. Furthermore, CD39 and CD73 expression on intra-hepatic B-cells was decreased in inflammatory livers. In vitro, B-cells from CHB patients showed a markedly reduced capacity to generate CD39/CD73-dependent extracellular adenosine and expressed increased levels of activation markers after adenosine-production blockade. Contrastingly, metformin significantly reduced activation-marker expression via regulating AMP-activated protein kinase.

Conclusions

The skewed CD39 and CD73 expression on B-cells was associated with a high viral burden, liver inflammation, and antiviral efficacy in CHB patients, and the skewed CD39/CD73/adenosine pathway contributed to B-cell hyperactivation. Regulation of the CD39/CD73/adenosine pathway using metformin may represent a therapeutic option to reverse HBV-induced immune pathogenesis.

Dysregulation in B-cell responses and T follicular helper cell function in ADA2 deficiency patients

Adenosine deaminase 2 deficiency (DADA2) is an autoinflammatory disease characterized by inflammatory vasculopathy, early strokes associated often with hypogammaglobulinemia. Pure red cell aplasia, thrombocytopenia, and neutropenia have been reported. The defect is due to biallelic loss of function of ADA2 gene, coding for a protein known to regulate the catabolism of extracellular adenosine. We therefore investigated immune phenotype and B- and T-cell responses in 14 DADA2 patients to address if ADA2 mutation affects B- and T-cell function. Here, we show a significant decrease in memory B cells, in particular class switch memory, and an expansion of CD21^low B cells in DADA2 patients. In vitro stimulated B lymphocytes were able to secrete nonfunctional ADA2 protein, suggesting a cell intrinsic defect resulting in an impairment of B-cell proliferation and differentiation. Moreover, CD4⁺ and CD8⁺ T cells were diminished; however, the frequency of circulating T follicular helper cells was significantly increased but they had an impairment in IL-21 production possibly contributing to an impaired B cell help. Our findings suggest that ADA2 mutation could lead to a B-cell intrinsic defect but also to a defective Tfh cell function, which could contribute to the immunodeficient phenotype reported in DADA2 patients.

Targeting CD73 to augment cancer immunotherapy

CD73 (ecto-5'-nucleotidase) is a novel immunoinhibitory protein that plays a key role for tumor growth and metastasis. Its main function is to convert extracellular ATP to immunosuppressive adenosine in concert with CD39 in normal tissues to limit excessive immune response. However, tumors take advantage of the CD73-mediated adenosinergic mechanism to protect them from immune attack. In particular, inducible expression of CD73 along with other adenosinergic molecules on both cancer cells and host cells sustains immunosuppressive tumor microenvironment by affecting multiple aspects of the immune response. Owing to its multifaceted capacity to tumor promotion as an emerging immune checkpoint, CD73 is an ideal therapeutic target for cancer treatment especially in combination with conventional therapy and/or other immune checkpoint inhibitors. In this review, we will discuss the roles of CD73 on tumor and immune cells and will highlight the therapeutic value of CD73 for combination therapy.

Rethinking mucosal antibody responses: IgM, IgG and IgD join IgA

Humoral immune responses at mucosal surfaces have historically focused on IgA. Growing evidence highlights the complexity of IgA-inducing pathways and the functional impact of IgA on mucosal commensal bacteria. In the gut, IgA contributes to the establishment of a mutualistic host-microbiota relationship that is required to maintain homeostasis and prevent disease. This Review discusses how mucosal IgA responses occur in an increasingly complex humoral defence network that also encompasses IgM, IgG and IgD. Aside from integrating the protective functions of IgA, these hitherto neglected mucosal antibodies may strengthen the communication between mucosal and systemic immune compartments.

A novel proangiogenic B cell subset is increased in cancer and chronic inflammation

B cells contribute to immune responses through the production of immunoglobulins, antigen presentation, and cytokine production. Several B cell subsets with distinct functions and polarized cytokine profiles have been reported. In this study, we used transcriptomics analysis of immortalized B cell clones to identify an IgG4⁺ B cell subset with a unique function. These B cells are characterized by simultaneous expression of proangiogenic cytokines including VEGF, CYR61, ADM, FGF2, PDGFA, and MDK. Consequently, supernatants from these clones efficiently promote endothelial cell tube formation. We identified CD49b and CD73 as surface markers identifying proangiogenic B cells. Circulating CD49b⁺CD73⁺ B cells showed significantly increased frequency in patients with melanoma and eosinophilic esophagitis (EoE), two diseases associated with angiogenesis. In addition, tissue-infiltrating IgG4⁺CD49b⁺CD73⁺ B cells expressing proangiogenic cytokines were detected in patients with EoE and melanoma. Our results demonstrate a previously unidentified proangiogenic B cell subset characterized by expression of CD49b, CD73, and proangiogenic cytokines.

Induction of metabolic quiescence defines the transitional to follicular B cell switch

Transitional B cells must actively undergo selection for self-tolerance before maturing into their resting follicular B cell successors. We found that metabolic quiescence was acquired at the follicular B cell stage in both humans and mice. In follicular B cells, the expression of genes involved in ribosome biogenesis, aerobic respiration, and mammalian target of rapamycin complex 1 (mTORC1) signaling was reduced when compared to that in transitional B cells. Functional metabolism studies, profiling of whole-cell metabolites, and analysis of cell surface proteins in human B cells suggested that this transition was also associated with increased extracellular adenosine salvage. Follicular B cells increased the abundance of the cell surface ectonucleotidase CD73, which coincided with adenosine 5'-monophosphate-activated protein kinase (AMPK) activation. Differentiation to the follicular B cell stage in vitro correlated with surface acquisition of CD73 on human transitional B cells and was augmented with the AMPK agonist, AICAR. Last, individuals with gain-of-function PIK3CD (PI3Kδ) mutations and increased pS6 activation exhibited a near absence of circulating follicular B cells. Together, our data suggest that mTORC1 attenuation may be necessary for human follicular B cell development. These data identify a distinct metabolic switch during human B cell development at the transitional to follicular stages, which is characterized by an induction of extracellular adenosine salvage, AMPK activation, and the acquisition of metabolic quiescence.

The CD73/Ado System-A New Player in RT Induced Adverse Late Effects

Radiotherapy (RT) is a central component of standard treatment for many cancer patients. RT alone or in multimodal treatment strategies has a documented contribution to enhanced local control and overall survival of cancer patients, and cancer cure. Clinical RT aims at maximizing tumor control, while minimizing the risk for RT-induced adverse late effects. However, acute and late toxicities of IR in normal tissues are still important biological barriers to successful RT: While curative RT may not be tolerable, sub-optimal tolerable RT doses will lead to fatal outcomes by local recurrence or metastatic disease, even when accepting adverse normal tissue effects that decrease the quality of life of irradiated cancer patients. Technical improvements in treatment planning and the increasing use of particle therapy have allowed for a more accurate delivery of IR to the tumor volume and have thereby helped to improve the safety profile of RT for many solid tumors. With these technical and physical strategies reaching their natural limits, current research for improving the therapeutic gain of RT focuses on innovative biological concepts that either selectively limit the adverse effects of RT in normal tissues without protecting the tumor or specifically increase the radiosensitivity of the tumor tissue without enhancing the risk of normal tissue complications. The biology-based optimization of RT requires the identification of biological factors that are linked to differential radiosensitivity of normal or tumor tissues, and are amenable to therapeutic targeting. Extracellular adenosine is an endogenous mediator critical to the maintenance of homeostasis in various tissues. Adenosine is either released from stressed or injured cells or generated from extracellular adenine nucleotides by the concerted action of the ectoenzymes ectoapyrase (CD39) and 5′ ectonucleotidase (NT5E, CD73) that catabolize ATP to adenosine. Recent work revealed a role of the immunoregulatory CD73/adenosine system in radiation-induced fibrotic disease in normal tissues suggesting a potential use as novel therapeutic target for normal tissue protection. The present review summarizes relevant findings on the pathologic roles of CD73 and adenosine in radiation-induced fibrosis in different organs (lung, skin, gut, and kidney) that have been obtained in preclinical models and proposes a refined model of radiation-induced normal tissue toxicity including the disease-promoting effects of radiation-induced activation of CD73/adenosine signaling in the irradiated tissue environment. However, expression and activity of the CD73/adenosine system in the tumor environment has also been linked to increased tumor growth and tumor immune escape, at least in preclinical models. Therefore, we will discuss the use of pharmacologic inhibition of CD73/adenosine-signaling as a promising strategy for improving the therapeutic gain of RT by targeting both, malignant tumor growth and adverse late effects of RT with a focus on fibrotic disease. The consideration of the therapeutic window is particularly important in view of the increasing use of RT in combination with various molecularly targeted agents and immunotherapy to enhance the tumor radiation response, as such combinations may result in increased or novel toxicities, as well as the increasing number of cancer survivors.

Ectonucleotidases in Blood Malignancies: A Tale of Surface Markers and Therapeutic Targets

Leukemia develops as the result of intrinsic features of the transformed cell, such as gene mutations and derived oncogenic signaling, and extrinsic factors, such as a tumor-friendly, immunosuppressed microenvironment, predominantly in the lymph nodes and the bone marrow. There, high extracellular levels of nucleotides, mainly NAD⁺ and ATP, are catabolized by different ectonucleotidases, which can be divided in two families according to substrate specificity: on one side those that metabolize NAD⁺, including CD38, CD157, and CD203a; on the other, those that convert ATP, namely CD39 (and other ENTPDases) and CD73. They generate products that modulate intracellular calcium levels and that activate purinergic receptors. They can also converge on adenosine generation with profound effects, both on leukemic cells, enhancing chemoresistance and homing, and on non-malignant immune cells, polarizing them toward tolerance. This review will first provide an overview of ectonucleotidases expression within the immune system, in physiological and pathological conditions. We will then focus on different hematological malignancies, discussing their role as disease markers and possibly pathogenic agents. Lastly, we will describe current efforts aimed at therapeutic targeting of this family of enzymes.

Ionizing radiation effects on the tumor microenvironment

The broad use of radiotherapy (RT) in the management of solid human tumors is based on its ability to damage cellular macromolecules, particularly the DNA, effectively inducing growth arrest and cell death locally in irradiated tumor cells. However, bystander effects, such as the transmission of lethal signals between cells via gap junctions or the production of diffusible cytotoxic mediators, can also contribute to the local antineoplastic action of RT. Traditionally, RT has been considered to exert immunosuppressive effects on the host. This idea largely stems from the radiosensitivity of quiescent lymphocytes and on the use of total body irradiation as part of myeloablative conditioning regimens preceding hematopoietic stem cell transplantation. Additionally, the occurrence of the so-called "abscopal effect," where nonirradiated distant lesions display effects of RT response, suggests that RT may also induce tumor immunization. Several RT-induced effects on cancer, immune and stromal cells, contribute to the abscopal effect: (1) induction of "immunogenic cell death", with release of tumor-associated antigens, (2) alterations of cancer cell immunophenotype, and (3) modulation of the tumor microenvironment. Damage and death of cancer cells leads to the surface exposure of immunogenic molecules as well as the release of damage associated molecular patterns such as adenosine triphosphate or High-Mobility-Group-Protein B1, and potentially tumor antigens that activate the innate and adaptive immune systems. Moreover, nuclear release and cytoplasmic sensing of altered nucleic acids via cyclic GMP-AMP Synthase/Stimulator of Interferon Genes is connected to the secretion of cytokines that support innate and adaptive antitumor immunity. As a result of the above, irradiated tumor cells may potentially act as an "in situ vaccine."

Targeting the Immunomodulatory CD73/Adenosine System to Improve the Therapeutic Gain of Radiotherapy

Extracellular adenosine is a potent endogenous immunosuppressive mediator critical to the maintenance of homeostasis in various normal tissues including the lung. Adenosine is either released from stressed or injured cells or generated from extracellular adenine nucleotides by the concerted action of the ectoenzymes ectoapyrase (CD39) and 5′ ectonucleotidase (CD73) that catabolize ATP to adenosine. An acute CD73-dependent increase of adenosine in normal tissues mostly exerts tissue protective functions whereas chronically increased adenosine-levels in tissues exposed to DNA damaging chemotherapy or radiotherapy promote pathologic remodeling processes and fibrosis for example in the skin and the lung. Importantly, cancer cells also express CD73 and high CD73 expression in the tumor tissue has been linked to poor overall survival and recurrence free survival in patients suffering from breast and ovarian cancer. CD73 and adenosine support growth-promoting neovascularization, metastasis, and survival in cancer cells. In addition, adenosine can promote tumor intrinsic or therapy-induced immune escape by various mechanisms that dampen the immune system. Consequently, modulating CD73 or cancer-derived adenosine in the tumor microenvironment emerges as an attractive novel therapeutic strategy to limit tumor progression, improve antitumor immune responses, avoid therapy-induced immune deviation, and potentially limit normal tissue toxicity. However, the role of CD73/adenosine signaling in the tumor and normal tissue responses to radiotherapy and its use as therapeutic target to improve the outcome of radiotherapy approaches is less understood. The present review will highlight the dual role of CD73 and adenosine in tumor and tissue responses to radiotherapy with a special focus to the lung. It will also discuss the potential benefits and risks of pharmacologic modulation of the CD73/adenosine system to increase the therapeutic gain of radiotherapy or combined radioimmunotherapy in cancer treatment.

Human Memory B Cells Harbor Diverse Cross-Neutralizing Antibodies against BK and JC Polyomaviruses

Human polyomaviruses cause a common childhood infection worldwide and typically elicit a neutralizing antibody and cellular immune response, while establishing a dormant infection in the kidney with minimal clinical manifestations. However, viral reactivation can cause severe pathology in immunocompromised individuals. We developed a high-throughput, functional antibody screen to examine the humoral response to BK polyomavirus. This approach enabled the isolation of antibodies from all peripheral B cell subsets and revealed the anti-BK virus antibody repertoire as clonally complex with respect to immunoglobulin sequences and isotypes (both IgM and IgG), including a high frequency of monoclonal antibodies that broadly neutralize BK virus subtypes and the related JC polyomavirus. Cryo-electron microscopy of a broadly neutralizing IgG single-chain variable fragment complexed with BK virus-like particles revealed the quaternary nature of a conserved viral epitope at the junction between capsid pentamers. These features unravel a potent modality for inhibiting polyomavirus infection in kidney transplant recipients and other immunocompromised patients.

Signaling control of antibody isotype switching

Class switch recombination (CSR) generates isotype-switched antibodies with distinct effector functions essential for mediating effective humoral immunity. CSR is catalyzed by activation-induced deaminase (AID) that initiates DNA lesions in the evolutionarily conserved switch (S) regions at the immunoglobulin heavy chain (Igh) locus. AID-initiated DNA lesions are subsequently converted into DNA double stranded breaks (DSBs) in the S regions of Igh locus, repaired by non-homologous end-joining to effect CSR in mammalian B lymphocytes. While molecular mechanisms of CSR are well characterized, it remains less well understood how upstream signaling pathways regulate AID expression and CSR. B lymphocytes express multiple receptors including the B cell antigen receptor (BCR) and co-receptors (e.g., CD40). These receptors may share common signaling pathways or may use distinct signaling elements to regulate CSR. Here, we discuss how signals emanating from different receptors positively or negatively regulate AID expression and CSR.

Common variable immune deficiency: Dissection of the variable

Starting about 60 years ago, a number of reports appeared that outlined the severe clinical course of a few adult subjects with profound hypogammaglobinemia. Puzzled by the lack of family history and adult onset of symptoms in most, the name "acquired" hypogammaglobinemia was given, but later altered to the current name common variable immune deficiency. Pathology reports remarked on the loss of lymph node architecture and paucity of plasma cells in lymphoid tissues in these subjects. While characterized by reduced serum IgG and IgA and often IgM, and thus classified among the B-cell defects, an increasing number of cellular defects in these patients have been recognized over time. In the early years, severe respiratory tract infections commonly led to a shortened life span, but the wide spread availability of immune globulin concentrates for the last 25 years has improved survival. However, chronic non-infectious inflammatory and autoimmune conditions have now emerged as challenging clinical problems; these require further immunologic understanding and additional therapeutic measures. Recent study of this phenotypic syndrome have provided an increasingly fertile ground for the identification of autosomal recessive and now more commonly, autosomal dominant gene defects which lead to the loss of B-cell development in this syndrome.

Association of Diverse Genotypes and Phenotypes of Immune Cells and Immunoglobulins With the Course of HIV-1 Infection

Disease progression among HIV-1-infected individuals varies widely, but the mechanisms underlying this variability remains unknown. Distinct disease outcomes are the consequences of many factors working in concert, including innate and adaptive immune responses, cell-mediated and humoral immunity, and both genetic and phenotypic factors. Current data suggest that these multifaceted aspects in infected individuals should be considered as a whole, rather than as separate unique elements, and that analyses must be performed in greater detail in order to meet the requirements of personalized medicine and guide optimal vaccine design. However, the wide adoption of antiretroviral therapy (ART) influences the implementation of systematic analyses of the HIV-1-infected population. Consequently, fewer data will be available for acquisition in the future, preventing the comprehensive investigations required to elucidate the underpinnings of variability in disease outcome. This review seeks to recapitulate the distinct genotypic and phenotypic features of the immune system, focusing in particular on comparing the surface proteins of immune cells among individuals with different HIV infection outcomes.

CD73-A2a adenosine receptor axis promotes innate B cell antibody responses to pneumococcal polysaccharide vaccination

Many individuals at risk of streptococcal infection respond poorly to the pneumococcal polysaccharide vaccine Pneumovax 23. Identification of actionable pathways able to enhance Pneumovax responsiveness is highly relevant. We investigated the contribution of the extracellular adenosine pathway regulated by the ecto-nucleotidase CD73 in Pneumovax-induced antibody responses. Using gene-targeted mice, we demonstrated that CD73-or A2a adenosine receptor deficiency significantly delayed isotype switching. Nevertheless, CD73- or A2aR- deficient adult mice ultimately produced antigen-specific IgG3 and controlled Streptococcus pneumoniae infection as efficiently as wild type (WT) mice. Compared to adults, young WT mice failed to control S. pneumoniae infection after vaccination and this was associated with lower levels of CD73 on innate B cells. We hypothesized that pharmacological activation of A2a receptor may improve Pneumovax 23 immunization in young WT mice. Remarkably, administration of the A2a adenosine receptor agonist CGS 21680 significantly increased IgG3 responses and significantly enhanced survival after S. pneumoniae challenge. Our study thus suggests that pharmacological activation of the A2a adenosine receptor could improve the efficacy of Pneumovax 23 vaccination in individuals at risk of streptococcal infection.

CD73 expression identifies a subset of IgM+ antigen-experienced cells with memory attributes that is T cell and CD40 signalling dependent

B-cell memory was long characterized as isotype-switched, somatically mutated and germinal centre (GC)-derived. However, it is now clear that the memory pool is a complex mixture that includes unswitched and unmutated cells. Further, expression of CD73, CD80 and CD273 has allowed the categorization of B-cell memory into multiple subsets, with combinatorial expression of the markers increasing with GC progression, isotype-switching and acquisition of somatic mutations. We have extended these findings to determine whether these markers can be used to identify IgM memory phenotypically as arising from T-dependent versus T-independent responses. We report that CD73 expression identifies a subset of antigen-experienced IgM⁺ cells that share attributes of functional B-cell memory. This subset is reduced in the spleens of T-cell-deficient and CD40-deficient mice and in mixed marrow chimeras made with mutant and wild-type marrow, the proportion of CD73⁺ IgM memory is restored in the T-cell-deficient donor compartment but not in the CD40-deficient donor compartment, indicating that CD40 ligation is involved in its generation. We also report that CD40 signalling supports optimal expression of CD73 on splenic T cells and age-associated B cells (ABCs), but not on other immune cells such as neutrophils, marginal zone B cells, peritoneal cavity B-1 B cells and regulatory T and B cells. Our data indicate that in addition to promoting GC-associated memory generation during B-cell differentiation, CD40-signalling can influence the composition of the unswitched memory B-cell pool. They also raise the possibility that a fraction of ABCs may represent T-cell-dependent IgM memory.

The ectonucleotidases CD39 and CD73: Novel checkpoint inhibitor targets

Cancers are able to grow by subverting immune suppressive pathways, to prevent the malignant cells as being recognized as dangerous or foreign. This mechanism prevents the cancer from being eliminated by the immune system and allows disease to progress from a very early stage to a lethal state. Immunotherapies are newly developing interventions that modify the patient's immune system to fight cancer, by either directly stimulating rejection-type processes or blocking suppressive pathways. Extracellular adenosine generated by the ectonucleotidases CD39 and CD73 is a newly recognized "immune checkpoint mediator" that interferes with anti-tumor immune responses. In this review, we focus on CD39 and CD73 ectoenzymes and encompass aspects of the biochemistry of these molecules as well as detailing the distribution and function on immune cells. Effects of CD39 and CD73 inhibition in preclinical and clinical studies are discussed. Finally, we provide insights into potential clinical application of adenosinergic and other purinergic-targeting therapies and forecast how these might develop in combination with other anti-cancer modalities.

The ectonucleotidases CD39 and CD73: Novel checkpoint inhibitor targets

Cancers are able to grow by subverting immune suppressive pathways, to prevent the malignant cells as being recognized as dangerous or foreign. This mechanism prevents the cancer from being eliminated by the immune system and allows disease to progress from a very early stage to a lethal state. Immunotherapies are newly developing interventions that modify the patient's immune system to fight cancer, by either directly stimulating rejection-type processes or blocking suppressive pathways. Extracellular adenosine generated by the ectonucleotidases CD39 and CD73 is a newly recognized "immune checkpoint mediator" that interferes with anti-tumor immune responses. In this review, we focus on CD39 and CD73 ectoenzymes and encompass aspects of the biochemistry of these molecules as well as detailing the distribution and function on immune cells. Effects of CD39 and CD73 inhibition in preclinical and clinical studies are discussed. Finally, we provide insights into potential clinical application of adenosinergic and other purinergic-targeting therapies and forecast how these might develop in combination with other anti-cancer modalities.

The ectonucleotidases CD39 and CD73: Novel checkpoint inhibitor targets

Cancers are able to grow by subverting immune suppressive pathways, to prevent the malignant cells as being recognized as dangerous or foreign. This mechanism prevents the cancer from being eliminated by the immune system and allows disease to progress from a very early stage to a lethal state. Immunotherapies are newly developing interventions that modify the patient's immune system to fight cancer, by either directly stimulating rejection-type processes or blocking suppressive pathways. Extracellular adenosine generated by the ectonucleotidases CD39 and CD73 is a newly recognized "immune checkpoint mediator" that interferes with anti-tumor immune responses. In this review, we focus on CD39 and CD73 ectoenzymes and encompass aspects of the biochemistry of these molecules as well as detailing the distribution and function on immune cells. Effects of CD39 and CD73 inhibition in preclinical and clinical studies are discussed. Finally, we provide insights into potential clinical application of adenosinergic and other purinergic-targeting therapies and forecast how these might develop in combination with other anti-cancer modalities.

Regulation of humoral immunity by gut microbial products

The intestinal tract provides ideal niches for several different microbial species, which are collectively called the gut microbiota. A key host immune effector that controls the microbiota and prevents mucosal infection is IgA. Gut microbiota-derived factors are largely classified into molecular pattern recognition receptor ligands and nutrient-derived metabolites including short-chain fatty acids and adenosine triphosphate. Along with host-derived factors such as retinoic acid, various cytokines and cytokine-like molecules, gut microbial products profoundly shape B cell responses. Gut microbial products can directly regulate B cell activation and differentiation. They can also indirectly affect B cells through epithelial cells, T cells, and myeloid cell subsets. We highlight the various direct and indirect mechanisms by which microbial products regulate humoral immunity.

E-NPP3 controls plasmacytoid dendritic cell numbers in the small intestine

Extracellular adenosine 5'-triphosphate (ATP) performs multiple functions including activation and induction of apoptosis of many cell types. The ATP-hydrolyzing ectoenzyme ecto-nucleotide pyrophosphatase/phosphodiesterase 3 (E-NPP3) regulates ATP-dependent chronic allergic responses by mast cells and basophils. However, E-NPP3 is also highly expressed on epithelial cells of the small intestine. In this study, we showed that E-NPP3 controls plasmacytoid dendritic cell (pDC) numbers in the intestine through regulation of intestinal extracellular ATP. In Enpp3-/- mice, ATP concentrations were increased in the intestinal lumen. pDC numbers were remarkably decreased in the small intestinal lamina propria and Peyer's patches. Intestinal pDCs of Enpp3-/- mice showed enhanced cell death as characterized by increases in annexin V binding and expression of cleaved caspase-3. pDCs were highly sensitive to ATP-induced cell death compared with conventional DCs. ATP-induced cell death was abrogated in P2rx7-/- pDCs. Accordingly, the number of intestinal pDCs was restored in Enpp3-/- P2rx7-/- mice. These findings demonstrate that E-NPP3 regulates ATP concentration and thereby prevents the decrease of pDCs in the small intestine.

Regulation of the T Cell Response by CD39

The ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1, or CD39) catalyzes the phosphohydrolysis of extracellular ATP (eATP) and ADP (eADP) released under conditions of inflammatory stress and cell injury. CD39 generates AMP, which is in turn used by the ecto-5'-nucleotidase CD73 to synthesize adenosine. These ectonucleotidases have a major impact on the dynamic equilibrium of proinflammatory eATP and ADP nucleotides versus immunosuppressive adenosine nucleosides. Indeed, CD39 plays a dominant role in the purinergic regulation of inflammation and the immune response because its expression is influenced by genetic and environmental factors. We review the specific role of CD39 in the kinetic regulation of cellular immune responses in the evolution of disease. We focus on the effects of CD39 on T cells and explore potential clinical applications in autoimmunity, chronic infections, and cancer.

Regulation of allergic inflammation by the ectoenzyme E-NPP3 (CD203c) on basophils and mast cells

Adenosine 5'-triphosphate (ATP) is released from dying or damaged cells, as well as from activated cells. Once secreted, extracellular ATP induces several immune responses via P2X and P2Y receptors. Basophils and mast cells release ATP upon FcεRI-crosslinking, and ATP activates basophils and mast cells in an autocrine manner. Nucleotide-converting ectoenzymes, such as E-NTPD1, E-NTPD7, and E-NPP3, inhibit ATP-dependent immune responses by hydrolyzing ATP, thereby contributing to immune response regulation. E-NPP3 is a well-known activation marker for human basophils. E-NPP3's physiologic function has recently been disclosed in mice. E-NPP3 is rapidly induced on basophils and mast cells after FcεRI-crosslinking and hydrolyzes extracellular ATP on cell surfaces to prevent ATP-dependent excess activation of basophils and mast cells. In the absence of E-NPP3, basophils and mast cells are overactivated and mice suffer from severe chronic allergic inflammation. Thus, the ATP-hydrolyzing ectoenzymes E-NPP3 has a nonnegligible role in the regulation of basophil- and mast cell-mediated allergic responses.

Circulating Human Neonatal Naïve B Cells are Deficient in CD73 Impairing Purine Salvage

Background

Extracellular purines, in particular adenosine (Ado) and adenosine-triphosphate, are critical immunoregulatory molecules. Expression and activity of purine ecto-enzymes on B cells in neonatal and adult blood may influence their function and has been incompletely characterized.

Methods

Mononuclear cells were isolated from human neonatal (cord blood) or adult (peripheral blood) subjects and evaluated directly by flow cytometry for expression of purine ecto-enzymes. Additionally, B cell subsets were isolated from mononuclear cell fractions by fluorescence-activated cell sorting and gene transcription of purine ecto-enzymes (CD39 and CD73), Ado deaminase (ADA1), purine nucleoside phosphorylase, and select purine receptors (A2a) were evaluated by reverse transcription followed by qRT-PCR. Immuno-magnetic-bead isolated naïve B cells were evaluated for enzymatic activity by incubation with radio-labeled purines followed by thin-layer chromatography, and subsequent B cell Ado acquisition was evaluated by liquid scintillation quantitation of radio-labeled Ado uptake.

Results

Relative to their adult counterparts, neonatal circulating naïve B cells were markedly and selectively deficient in CD73 as observed by gene transcription, surface protein expression, and enzyme activity. Neonatal naïve B cell deficiency of CD73 expression significantly impaired their capacity to acquire extracellular purines for purine salvage.

Conclusion

Human neonatal circulating naïve B cells are selectively deficient in CD73, impairing extracellular purine acquisition and potentially contributing to impaired B cell responses in early life.

Rapid Proliferation and Differentiation of a Subset of Circulating IgM Memory B Cells to a CpG/Cytokine Stimulus In Vitro

Circulating human IgM expressing memory B cells have been incompletely characterized. Here, we compared the phenotype and in vitro functional response (capacity to proliferate and differentiate to antibody secreting cells) in response to CpG and a cytokine cocktail (IL-2, IL-6, and IL-10) of sorted naïve B cells, IgM memory B cells and isotype-switched circulating memory B cells. Compared to naïve B cells, IgM memory B cells had lower integrated mean fluorescence intensity (iMFI) of BAFF-R, CD38, CD73, and IL-21R, but higher iMFI of CD95, CD11c, TLR9, PD-1, and CD122. Compared to switched memory B cells, IgM memory B cells had higher iMFI of BAFF-R, PD-1, IL-21R, TLR9, and CD122, but lower iMFI of CD38, CD95, and CD73. Four days after receiving the CpG/cytokine cocktail, higher frequencies of IgM than switched memory B cells—and these in turn greater than naïve cells—proliferated and differentiated to antibody secreting cells. At this time point, a small percentage (median of 7.6%) of stimulated IgM memory B cells changed isotype to IgG. Thus, among the heterogeneous population of human circulating IgM memory B cells a subset is capable of a rapid functional response to a CpG/cytokine stimulus in vitro.

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.

Oil-in-Water Emulsion MF59 Increases Germinal Center B Cell Differentiation and Persistence in Response to Vaccination

Induction of persistent protective immune responses is a key attribute of a successful vaccine formulation. MF59 adjuvant, an oil-in-water emulsion used in human vaccines, is known to induce persistent high-affinity functional Ab titers and memory B cells, but how it really shapes the Ag-specific B cell compartment is poorly documented. In this study, we characterized the Ab- and Ag-specific B cell compartment in wild-type mice immunized with HlaH35L, a Staphylococcus aureus Ag known to induce measurable functional Ab responses, formulated with MF59 or aluminum salts, focusing on germinal centers (GC) in secondary lymphoid organs. Taking advantage of single-cell flow cytometry analyses, HlaH35L-specific B cells were characterized for the expression of CD38 and GL-7, markers of memory and GC, respectively, and for CD80 and CD73 activation markers. We demonstrated that immunization with MF59-, but not aluminum salt-adjuvanted HlaH35L, induced expanded Ag-specific CD73(+)CD80(-) GC B cells in proximal- and distal-draining lymph nodes, and promoted the persistence of GC B cells, detected up to 4 mo after immunization. In addition to increasing GC B cells, MF59-adjuvanted HlaH35L also increased the frequency of T follicular helper cells. This work extends previous knowledge regarding adaptive immune responses to MF59-adjuvanted vaccines, and, to our knowledge, for the first time an adjuvant used in human licensed products is shown to promote strong and persistent Ag-specific GC responses that might benefit the rational design of new vaccination strategies.