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What else can CD39 tell us?


Abstract and Figures

As the rate-limiting enzyme in ATP/ADP-AMP-adenosine pathway, CD39 would be a novel checkpoint inhibitor target in preventing adenosine-triggered immune-suppressive effect. In addition, CD39hi Tregs, but not CD25hi Tregs, exhibit sustained Foxp3 levels and functional abilities, indicating it could represent a new specific marker of Tregs. Similarly, inhibition of CD39 enzymatic function at the surface of tumor cells alleviates their immunosuppressive activity. Far from conclusive, present research revealed that CD39 also dephosphorylated and thus inactivated self- and pathogen-associated phosphoantigens of Vγ9Vδ2 T cells, which may be the most promising subpopulation for cellular vaccine. CD39 is also tightly related to Th17 cells and can be regarded as a Th17 cells marker. In this review, we focus on present research of CD39 ectoenzyme and provide insights into its clinical application.
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June 2017 | Volume 8 | Article 7271
published: 22 June 2017
doi: 10.3389/fimmu.2017.00727
Frontiers in Immunology |
Edited by:
Marco Idzko,
University Medical Center
Freiburg, Germany
Reviewed by:
Silvia Piconese,
Sapienza Università di
Roma, Italy
Michele Ardolino,
University of Ottawa,
Yan Kang;
Hong Li
Specialty section:
This article was submitted
to Cytokines and Soluble
Mediators in Immunity,
a section of the journal
Frontiers in Immunology
Received: 25April2017
Accepted: 08June2017
Published: 22June2017
ZhaoH, BoC, KangY and LiH
(2017) What Else Can CD39 Tell Us?
Front. Immunol. 8:727.
doi: 10.3389/fimmu.2017.00727
What Else Can CD39 Tell Us?
Hai Zhao1, Cong Bo1, Yan Kang1* and Hong Li2*
1 Department of Critical Care Medicine, West China Hospital, Sichuan University, Chengdu, China, 2 Key Laboratory of
Obstetrics & Gynecology, Pediatric Diseases, and Birth Defects of the Ministry of Education, West China Second Hospital,
Sichuan University, Chengdu, China
As the rate-limiting enzyme in ATP/ADP–AMP–adenosine pathway, CD39 would be a
novel checkpoint inhibitor target in preventing adenosine-triggered immune-suppressive
effect. In addition, CD39hi Tregs, but not CD25hi Tregs, exhibit sustained Foxp3 levels and
functional abilities, indicating it could represent a new specific marker of Tregs. Similarly,
inhibition of CD39 enzymatic function at the surface of tumor cells alleviates their immu-
nosuppressive activity. Far from conclusive, present research revealed that CD39 also
dephosphorylated and thus inactivated self- and pathogen-associated phosphoantigens
of Vγ9Vδ2 Tcells, which may be the most promising subpopulation for cellular vaccine.
CD39 is also tightly related to Th17cells and can be regarded as a Th17cells marker.
In this review, we focus on present research of CD39 ectoenzyme and provide insights
into its clinical application.
Keywords: CD39, extracellular ATP, adenosine, Tregs, γδ Tcell, CD161, Th17cell, Bregs
Extracellular adenosine and ATP exert important functions in physiology and pathophysiology.
ey for instance play key role in heart and vascular function, during pregnancy (1) and in immune
responses (2). Outside the cell, extracellular ATP (eATP) acts as danger-associated molecular pat-
terns (DAMPs) and can bind to purinergic receptors to trigger signaling cascades to induce an
inammatory response (3). However, adenosine is a potent immune-suppressor of cells that express
A2 and A3 receptors, such as lymphocytes (4). To avoid ATP-induced pathological eects, ATP can
be hydrolyzed into adenosine and phosphate by a cascade of enzymes, of which CD39 is the most
CD39, the NTPDase (ecto-nucleoside triphosphate diphosphohydrolase), regulates immune
responses balance by hydrolyzing ATP and ADP. It is now again becoming a newly recognized
“immune checkpoint mediator” that interferes with antitumor or anti-inammatory immune
response (5, 6). Moreover, some recent research has revealed a number of neoteric functions of
CD39, which display its close relation with Tregs (79), 17cells (10, 11), γδ Tcells (12), and Bregs
(13). It follows from this reasoning that CD39 acts as a key molecule in inammation (1416) and
tumor immunity (1720).
In the present review, we will discuss the current knowledge on the role of CD39 expressed on
dierent types of cells and explore its potential in inammation and tumor immunity.
Cellular ATP serves as the main energy currency, driving virtually all cell functions. Self-evidently,
intracellular ATP plays important pathophysiological roles. In terms of eATP, it is ubiquitously
used for cell–cell communication in physical setting. Low concentration of eATP-detected sur-
rounding resting cells indicates the presence of neighboring living cells, especially in nervous (21)
FIGURE 1 | Ectoenzymes, e.g., CD39, CD73 mediate the metabolization of
extracellular ATP (eATP) to adenosine. eATP signals through P2X and P2Y
purinergic receptors to induce inflammation while adenosine exerts
immunosuppressive activity on immune cells and thereby protects tissues
against excessive inflammation.
Zhao et al. CD39—An Unpolished Sword in Immunology Network
Frontiers in Immunology | June 2017 | Volume 8 | Article 727
and vascular systems (22). And also, this biochemical substance
can be poured into extracellular space upon, for instance, tissue
stress such as necrosis, apoptosis, hypoxia, or inammation
(23). Release from activated or apoptotic cells is done via two
mechanisms as follows: transport via membrane-bound chan-
nels or transporters and exocytosis of intracellular vesicles (24).
Additional work showed that kindred purinergic signaling
pathways regulate critical aspects of many other physiological
processes, including immune response (25).
Recent years, the role of eATP in immune system has broaden
our horizon. ATP release in response to inammatory mediators
is a basic mechanism required for neutrophil activation and
immune defense (26). e steady-state cytosolic concentration
of ATP is 3–10mM, whereas eATP is only~10nM (27), which
is maintained as a result of the activities of extracellular ecto-
apyrases and CD39. e enzymatic activities of CD39 and CD73
play paramount roles in calibrating the particularity, duration,
and magnitude of purinergic signals via the conversion of
ATP/ADP to AMP and AMP to adenosine, respectively. e
ATP-CD39–CD73–adenosine cascade is strictly controlled by
enzymatic activity, in which CD39 serves as the rate-limiting
enzyme (28).
Balance between eATP and adenosine (see Figure1) is crucial
in immune homeostasis since eATP is a danger signal released by
injured or apoptosis cells that acts to prime immune responses
through the ligation of P2 receptors (2). ere are two subsets
of P2 receptors: P2X or P2Y receptors (23). Seven P2X receptors
plus eight P2Y receptors have been identied in humans (26, 29).
Responses to low eATP are mediated by P2 receptors with high or
intermediate anity for eATP (EC50 <20µM), while responses
to high eATP are mediated by P2X7 (EC50 >100μM) (27). As
for a further explanation, eATP functions as DAMPs and then
binds to P2 receptors, resulting in heightened inammation and
regulatory cell inhibition in most cases (30).
ATP has varieties of pro-inammatory eects. Since sundry
immune cells express most of the ATP receptors, ATP can aect
most immune cells. For example, eATP released by damaged
cells can activate the immune system via the stimulation of P2X7
receptors on DCs and then promote the secretion of IL-1β and
IL-18 (31). Next, IL-1β will facilitate macrophages maturation and
their cytokine production increase (32). Similarly, IL-18 would
boost NK cells proliferation and strengthen IFN-γ production
plus cytotoxicity (33). While in Tcells, ATP activates Tcells by
inducing IL-2 production and cytotoxicity. Moreover, it induces
dierentiation toward pro-inammatory 17 cells, while it
inhibits the dierentiation toward Tregs. From a micro perspec-
tive, eATP stimulates Ca2+ entry through P2X purinergic receptor
channels and Ca2+ mobilization to facilitate Ca2+-calmodulin-
dependent activation and nuclear translocation of nuclear factor
of activated Tcells (NFAT), which stimulates the production of
IL-2, pannexin 1 channels, and other NFAT targets. Autocrine
ATP release helps to sustain P2 purinergic receptor signaling and
NFAT activation (34).
Adenosine—the counterpart of ATP, which is produced by
breakdown of ATP—is nothing of a novelty. As early as 1980s,
adenosine has been used to slow down the heart rate of patients
suering from supraventricular tachycardia (22). As for immune
system, rather than activating T cells responses, adenosine
conversely inhibits Tcells responses including Tregs and 
cells. But it is not contradictory that adenosine inhibits the
dierentiation toward 17cells while it promotes dierentia-
tion toward Tregs. It is actually regarded as a key endogenous
molecule that regulates tissue function by activating four
G-protein-coupled P1 receptors, denoted A1, A2A, A2B, and
A3 (35). A1 and A2A are high-anity receptors, while A2B and
A3 are low-anity receptors (36). Meanwhile, A2A and A2B
stimulate adenylyl cyclase, while A1 and A3 inhibit adenylyl
cyclase (36). P1 receptors are expressed on kinds of immune
cells such as macrophages, dendritic cells, and lymphocytes.
ere are now varieties of promising emerging therapeutic
approaches centered on the modulation of adenosine in the
immune system (37). Triggering dierent receptors can have
dierent consequence. Importantly, A2A receptors are closely
related to cyclic adenosine monophosphate (cAMP) response
element-binding protein, which eventually leads to the tran-
scription of the CEBPβ gene (38). While CEBPβ protein binds
to the IL-10 gene promoter, which triggers IL-10 transcription,
and subsequently leads to the release of IL-10 (38). IL-10, human
cytokine synthesis inhibitory factor, was reported to suppress
cytokine secretion, antigen presentation, and CD4+ Tcell activa-
tion (39). One interesting research to mention is that resilient
individuals seem to have a better anti-inammatory response
compared to posttraumatic stress disorder patients since they
present higher IL-10 levels (40).
e ultimate eect of ATP and adenosine during immune
responses depends on the balance between the two molecules.
Of note, though CD39 and CD73 expressed on immune cells
decrease local ATP levels while increase local adenosine levels,
the substrate and catalytic product of ATP/ADP–CD39–AMP–
adenosine pathway, are not actually simple yin and yang in
immune responses (41). In fact, both ATP and adenosine may
have dual eects on immune responses, depending on concen-
tration, the duration of the exposure, and the conditions of the
invivo environment. Under pronged exposure or at low concen-
trations, as mentioned before, responses to eATP are mediated
by P2R with EC50 <20μM (41). en, it will reduce secretion of
inammatory cytokine including IL-1β, IL-6, IL-12, and TNF-α,
etc., of macrophages or mature DCs (42).
FIGURE 2 | Illustration of CD39 function eATP accumulates in the extracellular space in response to metabolic stress or cell damage such as apoptosis. CD39
initiates extracellular adenosine generation by catalyzing the degradation of ATP and ADP to AMP; CD73 also has ecto-5-nucleotidase enzyme activity that catalyzes
the dephosphorylation of AMP to adenosine; CD39, not CD73, is the rate-limiting enzyme of the cascade leading to the generation of suppressive adenosine.
Adenosine activates A2A receptor and subsequently triggers pathways converge on CEBPβ to induce IL10 production. CD39 also dephosphorylates pAgs of
Vγ9Vδ2 Tcells. This degradation may also be catalyzed by CD39 expressed on Tregs and possibly represents a novel mechanism of Tregs suppressing Vγ9Vδ2
Tcells. CD39 upregulation acts as a feedback mechanism to desensitize Vγ9Vδ2 Tcells to self- and pathogen-associated pAgs. Pro-apoptotic Bim, antiapoptotic
Mcl-1, and apoptotic regulators Bax and Bak altogether contribute to Tcells homeostasis and survival. Especially, IL-2 and costimulatory signals upregulate Mcl-1
expression and hence allows Tregs to proliferate. We speculate that CD39 is involved in the above signal transduction since CD39 were reported to be associated
with Tcells apoptosis.
Zhao et al. CD39—An Unpolished Sword in Immunology Network
Frontiers in Immunology | June 2017 | Volume 8 | Article 727
CD39 and Tregs
Tregs play an indispensable role in maintaining immunological
unresponsiveness to self-antigens and in suppressing excessive
immune responses deleterious to the host. In order to better
explain the relationship between CD39 and Tregs, it is necessary
to make sense of how Tregs work?
We must realize that there is still a long way to gure out the
comprehensive mechanism of Tregs. e molecular mechanisms
of suppression remain incompletely understood and even all the
present conclusions are not agreed at all. A variety of molecules
are involved in Treg-mediated suppression mechanisms, includ-
ing IL-2, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4),
glucocorticoid induced tumor necrosis factor receptor (GITR),
IL-10, TGF-β, IL-35, LAG3 (lymphocyte-activation gene3),
granzyme B, adenosine, and cAMP (43). Given that ectopic
Foxp3 expression in conventional Tcells can function Treg-like
suppressive activity, the molecule(s) mediating a core suppres-
sive mechanism may well be controlled by Foxp3 (4446). Foxp3
indeed dominates the expression of the above molecules and
deciencies of these molecules would produce similar autoim-
mune diseases as observed in Foxp3 deciency (43, 47). We are
not going to discuss the intricate mechanisms here in detail, but
we are glad to introduce some recent research on the progress.
ere has been some research focused on apoptotic mecha-
nism of Tregs recently. It was found that Tregs proliferate more
rapidly than other CD4+CD25 conventional T cells under a
static condition (48). Mcl-1, a member of Bcl-2 protein family
(49, 50), is the dominant antiapoptotic in maintaining their
dynamic changes—Tregs will proliferate aer IL-2 elevates antia-
poptotic Mcl-1 expression. Mcl-1 in turn inhibits Bax-mediated
intrinsic apoptotic pathway and hence allows Tregs to proliferate
in another way (48). Moreover, Fang etal. reported that CD39 not
only can identify human CD4+ Tcells prone to apoptosis but it is
more readily induced in CD4+ Tcell response of elder individual
(51). CD39 may also play a key role in Tregs homeostatic bal-
ance and the relationship between CD39 and apoptosis deserves
further study (see Figure2).
CD39 has been reported to be found on the surface of human and
murine naive Tregs (52, 53). e ATP–CD39–CD73–adenosine
axis contributes to Foxp3+ CD4+ suppressor Tcell activity (54).
A subset of CD4+ Tcells express CD39 combined with CD25,
TABLE 1 | Antigens stimulating different subsets of γδ Tcells.
δ chain
γ chain
Distribution Antigens/
Vδ1 Vγ (several) Skin, gut,
tract, PB,
spleen, liver
CD1c, CD1d,
HLA-A24, HLA-A2,
tetanus toxoid,
Hsp60, Hsp65
Vδ3 Vγ9/3 PB, liver CD1d (78)
Vδ5 Vγ4 PB EPCR (79)
PB, peripheral blood; MICA or MICB, MHC class I chain-related protein A or B;
CD1c or CD1d, cluster of differentiation 1 isoforms; HLA, human leukocyte antigen;
IPP, isopentenyl pyrophosphate; HMBPP, (E)-4-hydroxy-3-methyl-but-2-enyl
pyrophosphate; Hsp, heat-shock protein; EPCR, endothelial protein C receptor.
Zhao et al. CD39—An Unpolished Sword in Immunology Network
Frontiers in Immunology | June 2017 | Volume 8 | Article 727
GITR, and CTLA-4 molecules, which are commonly found on
Foxp3+CD4+ Tcells (55). More importantly, CD39+ CD4+Tcells
do express Foxp3. Indeed, A2A receptors (the main adenosine
receptors) stimulation inhibits IL-6 expression while promoting
TGF-β production (56). Antigenic stimulation of naïve Tcells in
the presence of TGF-β leads to FOXP3 expression, and conse-
quently, Tregs function (57). us, upon binding to A2A recep-
tors, adenosine not only suppresses eector Tcells functions but
also promotes the induction of adaptive Tregs.
Interestingly, CD39 has so far only been known as an ecto-
ATPase. But, Gruenbacher etal. proved that CD39 also dephos-
phorylates and thus inactivates self- and pathogen-associated
phosphoantigens (12). We speculate that hydrolyzing specic
antigens would also be another option by which Tregs functions,
at least for Vg9Vd2 Tcells. An experiment designed to conrm
this mechanism of Treg is now being conducted in our laboratory.
At this stage, Tregs are still puried dependent on the expression
level of CD25—CD4+CD25+, CD4+CD25high, or CD4+CD25high
FOXP3+. Considering that CD25 (IL-2Rα) is also widely expressed
on eector lymphocyte besides Treg, it is not an ideal surface
marker actually. It has been conrmed that CD39 is predominantly
expressed on human CD4+ Foxp3+ Tcells, and that its expression
level is proportional to the Foxp3 expression level (52). us, CD39
can be a competent surface marker for routine isolation of func-
tionally active human Tregs from the peripheral blood of healthy
donors or patients. In addition, CD39 expression is considered null
in Foxp3+CD4+ T cell development since CD39-decient mice
still possess peripheral CD4+CD25+ T cells. But the conclusion
has limitations because CD39-knockout may just induced another
equally critical detour pathway during Treg development and
maybe both of them cannot work at the same time.
Of note, we should be aware of not all human CD4+ FOXP3+
T cells-expressing CD39. e proportion of this subset dra-
matically changes depending on ages (51) or diseases (52, 58,
59), indicating that CD39 expression to some degree might be
of diagnostic interest. In addition, there is also a subset of CD4+
CD39+ T cells with lacking immunosuppressive function in
peripheral blood (60). Actually, CD4+ CD39+ CD25neg FOXP3neg
subset can be regarded as a reservoir of CD39+ Tregs since the
former can be transformed into the latter upon staphylococcal
enterotoxin B stimulation (61). erefore, CD39 may be an
indispensable chip to identify Tregs, but not absolutely unique.
CD39 and γδ T Cell
ree decades have passed since the accidental but groundbreak-
ing discovery of Tcells expressing γ and δ chains in 1984 (62). But
in the early stages, these immune cells were thought to be null and
were suspiciously ill-represented in textbooks (62). e reasons
for this negligence were majorly due to technical and conceptual
diculties in our understanding—how γδ Tcells are generated
in the thymus, which type of target structures they recognize,
what the contributions they make to homeostasis, and when they
take up action facing foreign pathogen or self antigen? γδ Tcells
belong to the non-conventional lymphocyte family though they
can produce many cytokines of the same kind as αβ Tcells such as
IFN-γ, IL-17, and bear certain cell surface markers. But they are
in possession of combination of cytotoxic function (63), follicular
B helper function (64), antigen presentation function (65, 66),
and regulatory functions (20, 67). Gδ T-APC, in particular, may
represent a promising alternative to monocyte-derived dendritic
cell in immunotherapy since γδ T-APC lack MHC restriction
in antigen recognition and they are so easy to expand in large
scale (68). Maybe it is not easy to categorize γδ Tcells—are they
regulatory cells, follicular B helper cells, cytotoxic cells, APC,
or totipotent cell? is is indeed the case that γδ Tcells share
pleiotropic functions with conventional αβ Tcells (69). As the
research work goes further and more detailed, the classication of
γδ T would be more reasonable. Maybe γδ Tcells are composed
of dierent subpopulations with dierent functions (see Tabl e 1).
Human γδ TCR-expressing cells constitute 1–5% of total
Tcells in the peripheral blood but make up a major lymphoid
subset in tissues such as the intestine and the dermis (80).
Human Vδ1 Tcells primarily reside in the dermis, gut epithelia,
and are involved in maintaining epithelial tissue integrity (81).
Vγ9Vδ2 (also termed as Vγ2Vδ2) T cells are a subset of γδ
Tcells in the peripheral circulation and play an indispensable
role in host defenses against exogenous pathogens, immune sur-
veillance of endogenous pathogenesis, and even homeostasis of
the immune system. Recent researches have shown that CD277
plays a leading role (82) in Vγ9Vδ2 T activation and also CD39
on them is an important surface marker (8). Both of mice naïve
and induced CD39+ γδ T cells expressed CD25 rather than
FOXP3 nor CTLA-4, but have a stronger suppressive function
via IL-10 (8). Recently, Hu et al. has identied a novel γδ-Treg
subset exhibiting CD39 with stronger immunosuppressive activ-
ity than conventional CD4+ or CD8+ Tregs. More importantly,
this CD39+ γδ-Tregs perform their suppressive function via the
adenosine-induced pathway instead of TGF-β or IL-10 (20).
Herein, we highlight a recent study by Gruenbacher etal. who
proved CD39 also hydrolyzes pAgs (phosphoantigens) which
specically activate Vγ9Vδ2 T cells (12) and thus revealed a
previously unrecognized immune-regulatory role of CD39. By
quantifying Pi in supernatant aer incubating Vγ9Vδ2 Tcells
with dierent pAgs, the hydrolysis function of CD39 displays a
cell dose-, substrate-, and time-dependent manner. Interestingly,
FIGURE 3 | CD39 is involved in Th17cells expansion and IL-17 secretion and, moreover, CD4+CD39+CD161+ Tcells can be regarded as Th17cells precursors.
CD39, combined with CD161, can initiate acid sphingomyelinase enzymatic activity, subsequently, increase intracellular ceramide concentration, then impact STAT3
and mTOR signal transduction, which are essential for Th17 generation and IL-17 secretion.
Zhao et al. CD39—An Unpolished Sword in Immunology Network
Frontiers in Immunology | June 2017 | Volume 8 | Article 727
geranylgeranyl diphosphate (GGPP, C20), which can also activate
Vγ9Vδ2 Tcells, resists CD39-mediated hydrolysis. us, GGPP,
not other pAgs, would be exploited as a novel checkpoint for
increasing the stability of ATP and pAgs (see Figure2).
CD39 and Th17 Cells
Recently, Bai et al. reported that another novel ndings that
CD39 combined with CD161 drives 17 cells expansion via
acid sphingomyelinase (ASM) in Crohns disease patients (83).
is conclusion, again, refresh our knowledge about CD39.
17 cells are critical for host protective defense in adaptive
immune responses and autoimmune diseases (84). But how CD4+
Tcells polarize into 17cells subset is still a maze in addition
to their lacking convincing surface marker. Bai etal. presented
a novel notion that CD4+CD39+CD161+ can be used as 17
precursors surface marker. Besides MHC/CD3/CD28 and IL-6/
IL-6R pathway, CD39/CD161-ASM amplies mTOR and STAT3
signals in another way, which eventually drive 17cells expan-
sion and, subsequently, IL-17 secretion. Given the signicance of
17cells, strategies to regulate CD39 and CD161 signaling may
represent another novel approach to suppress 17 responsive-
ness of inammatory disease (see Figure3).
CD39 and Other Immune Cells
Indeed, CD39 was rst described as a B lymphocyte activation
marker (20, 85) and then be regarded as a Tlymphocyte activa-
tion marker (86, 87). It is constitutively expressed on >90% of
Bcells, >90% of monocytes, 20–30% of CD4+ Tcells (including
memory Tcells and Tregs), <5% of CD8+ Tcells, and 2–5% of
NKcells (6).
High-level expression of CD39 indicates CD8+ T cells
terminally exhaustion especially in chronic viral infections,
but it is not applicable to the CD8+ T cell compartment of
healthy donors (88). In addition to be used as a marker of
terminally exhausted CD8+ T Cells, CD39 also participates in
the identication of CD8+CD39+CD26 cells—a specic subset
of CD8+ Tregs equipped with eective suppressive function
via nicotinamide adenine dinucleotide phosphate oxidase 2
(NOX2) (89).
CD39 plays an indispensable part in DCs-driven CD4+ Tcells
activation and dierentiation. For example, eATP activates the
NLLRP3 inammasome in DCs and this inammasome is a
prerequisite for the production of IL-1β and IL-18 (31). While the
abovementioned cytokines are essential for 17 and 1cells
polarization, respectively (90). As for 2 cells, Idzko etal. found
that DCs in Cd39 null mice showed weak capacity to induce 2
immunity (91). ey speculated that CD39-involved P2 receptors
signaling might facilitate DCs to prime 2 responses in vivo.
Indeed, NLLRP3 is also supposed to promote 2 cells polari-
zation although this process is not by means of inammasome
form (92). Furthermore, accumulation of adenosine can impair
the normal function of DCs, the so-called immune-suppressive
regulatory DCs (93).
NKcells belonging to innate immune subset are characterized
by mediating signicant cytotoxicity, producing high levels of
inammatory cytokines and chemokines (22, 94, 95). Human
NKcells can be modulated through activation of P2Y11R (20)
and, therefore, CD39 can inhibit NK cells-mediated damage.
ere is indeed the case that CD39 deletion has been followed
by the deciency of IFN-γ by NKcells. In the context of tumor
Zhao et al. CD39—An Unpolished Sword in Immunology Network
Frontiers in Immunology | June 2017 | Volume 8 | Article 727
setting, expression of CD39 with consequently ATP degradation
induced antitumor immune responses mediated by NKcells.
Human Bcells have been reported to express CD39 and adeno-
sine receptors (20). Figueiró etal. identied CD39high Bcells as the
major contributor to Bregs (13). ey also reported proliferation
and functions of these CD39high Bcells are operated via adenosine
generation and IL-10 secretion. Unlike previous research, the A1
and A2A adenosine receptors other than A3 adenosine receptor
mainly mediate autocrine signaling in Bregs.
e purinergic system is a high-level delicate system adjusted
to ne-tune immune cell functions. Varieties of cell types can
release ATP or ADP from intracellular compartments into the
extracellular spaces, besides apoptotic cells. eATP functions as a
dangerous signal triggering activation of purinergic P2 receptors
and hence subsequently a series of pro-inammation responses
(23, 96). is pro-inammation cascade is terminated by conver-
sion to suppressive molecule adenosine via CD39 and CD73.
Similar to ATP, adenosine activates purinergic P1 receptors.
During the process of inammation, there are also several patho-
genic microorganisms capable of inducing an adenosine-rich
milieu, which favors them to escape host immune surveillance.
By contrast, there is also evidence that overexpression of CD39
in mouse airways promotes bacteria-induced inammation (97).
e author speculated that CD39 might limit the desensitization
of P2 receptors, which helps to promote airway inammation in
response to bacterial challenge. Consistent with the above results,
CD39 expression and activity are elevated in chronic obstruc-
tive pulmonary disease (COPD) patients by quantifying CD39
expression and soluble ATPase activity in sputum and bron-
choalveolar lavage uid cells (98). Additionally, Tan etal. showed
Tcell-related CD39 expression is higher in acute exacerbations
of COPD (AECOPD) patients than stable COPD and healthy
controls (5). ey prospected blocking CD39 would be a novel
approach to the control of AECOPD, reducing the dependency
on antibiotics.
In addition, some microorganisms themselves are equipped
with high nucleotide metabolic versatility, which assist them
with dissemination and invasion in the host (99). For example,
Fan etal. reported that an ecto-5-nucleotidase similar to human
CD39 on cell surface of Streptococcus sanguinis contributes to its
virulence (100). is analog takes eects by means of slowing the
platelet aggregation response invitro and reducing the accumula-
tion of platelets on infected heart valves invivo (100).
Hence, CD39, a pivotal enzyme between ATP and adenosine,
is critical in preventing excessive P2R-mediated inammation,
but its function maybe turns detrimental for the appropriate
clearance of apoptotic debris or by generating an immunosup-
pressive environment, which might promote the development or
progression of cancer (101).
Interactions between tumor cells and their immunological
microenvironment are essential for the pathophysiology of
tumor (102). CD39, the rate-limiting enzyme in the generation
of immune-suppressive adenosine, undoubtedly plays a pivotal
role in tumor progression. For example, CD39+ Tregs, mentioned
above, inhibited NKcell antitumor immunity both invitro and
inviv o (20). Besides t his, CD39 is expressed at signicantly higher
rates in tumor-inltrating tissue such as ovarian, pancreatic, and
testicular tumors, etc., in contrast to paired peritumoral tissue
(55). Overexpression of CD39 was reported as a predictor of
poor outcome for gastric cancer patient following radical resec-
tion (103). Additionally, CD39 expressed on Tregs was shown
to play a permissive role in a mouse model of hepatic metastasis
(104). erefore, CD39 penetrates deep into to the modulation
of tumor cell growth, dierentiation, invasion, and migration
(105, 106).
Importantly, aer co-incubating these tumor cells with
POM-1, the CD39 inhibitor, tumor-induced inhibition of
CD4+ and CD8+ Tcell proliferation was alleviated and CTL- or
NK cell-mediated cytotoxicity increased. Consequently, treat-
ment with a CD39 inhibitor or blocking antibody may become
a promising strategy for ameliorating tumor cell-mediated
immunosuppression. ese data indicate CD39 to be a prob-
able checkpoint in tumor immunotherapy and inhibiting CD39
may restore antitumor responses or boost the ecacies of other
antitumor strategies. For example, treatment with ARL6715,
another ectoATPase inhibitor, resulted in improving T cell
responsiveness (107). e link between CD39 and tumor will
become clearer since tumor-related research focused on CD39
is emerging in endless stream.
e enzymatic activity of CD39, combined with CD73, plays
a non-ignorable part in the shi from an ATP-mediated pro-
inammatory milieu to an immunosuppressive setting driven
by adenosine. Some recent discovery about its new features such
as hydrolyzing pAgs and catalyzing sphingomyelin suggest that
CD39 have more unrecognized physical functions. Either way,
in-depth study of CD39 will provide unique insights into the
workings of immune network.
First, in basic research, CD39 can be considered as a novel
bridge among immune cells. It is expressed on varieties of
immune cells and there exists close relationship between CD39
and their functions. In the context of a subgroup, classication of
immune cells based on CD39 may reect their functions better.
It is remarkable that CD39 is increasingly appreciated as a regula-
tory marker other than an activation marker. We can identify not
only CD4+ Tregs but also CD8+ Tregs, Bregs, and γδ-Tregs based
on CD39. As for its newly known feature about hydrolyzing pAgs,
this may represent another mechanism by which CD4+ Tregs
suppress γδ Tcells. Besides “classical” functions such as cytokine
production and cytotoxicity, recent studies suggest that γδ Tcells
are equipped with additional eciencies such as regulatory activ-
ity (20) and—quite excitingly—“professional” antigen-presenting
capacity (108). We should breathe calmly that it is absolutely
worth a great number of costs on this fewer proportion.
Another emerging discovery about CD39 is closely related
to CD161—they altogether modulate human 17 cells
Zhao et al. CD39—An Unpolished Sword in Immunology Network
Frontiers in Immunology | June 2017 | Volume 8 | Article 727
responsiveness through alterations in ASM (10). CD39 and
CD161 serve as potent surface markers of 17cells (10, 11), and
furthermore, the latter has been identied as the top favorable
pan-cancer prognostic molecule (109). ere is still a long way
to go to expound on the connection between CD39 and CD161.
And what’s more, γδ Tcells are also found to be a very important
source of IL-17 in some disease models, particularly at early stage
(110). Whether CD39/CD161-ASM-IL-17 chain also exists in γδ
Tcells has not been evaluated. Additionally, expression of CD39
is particularly associated with exhaustion of CD8+ Tcells and
identication of CD8+ Tregs, Bregs, both of which are being in
the ascendant among immunological studies.
Second, the diagnostic potential of CD39 is only beginning to
unfold. ere have been already some studies proposing CD39
as a prognostic marker such as pancreatic cancer (105). In the
setting of chronic lymphocytic leukemia, both CD4+ Tcells and
CD8+ Tcells express high-level CD39 and furthermore, CD39 is
associated with advanced disease stage (111). Besides, CD39 is
also closely related to both 17cells and Tregs. In the context of
inammation or autoimmune diseases such as rheumatoid arthri-
tis, 17cells stand for a pro-inammatory subpopulation while
Tregs have the antagonist eect. Hence, the 17/Tregs balance
can aect the outcome of immune responses. CD39, surprisingly,
participates in the identication of both (see above). Fan etal.
proposed identifying CD4+ T cell-derived CD161+CD39+ and
CD39+CD73+ microparticles as new biomarkers for rheumatoid
arthritis evaluation (11).
Finally, immunotherapy will be the direction of our long-
term eorts and moreover, the possibly ultimate way out to
inammation and cancer. Immunomodulatory eects of CD39
brought a new dawn for immunotherapy. Since CD39 not only
hydrolyzes eATP but also increases the concentration of anti-
inammatory adenosine, the administration of exogenous CD39,
in nanoparticles or other forms may provide a new approach
to limiting inammation, which is likely to be more ecient
than existing strategies aimed at blocking P2X. Alternatively,
given the increased CD39 expression in apoptosis-prone Tcells
(51, 88), blocking CD39 with specic reagents might provide
a novel checkpoint to induce a reaction cascade of protective
responses in infection or tumor immunotherapy.
In summary, human immune system is a tight-knit social
network while CD39 has correlation to various immune cells. It is
now becoming increasingly appreciated that CD39 is a promising
therapeutic target. Increasing or inhibiting CD39 can interfere
with the abnormal pathophysiological process of disorders, espe-
cially inammation and tumor. We are hopeful that the extensive
impact of CD39 on the operation of immune response will be
profoundly illustrated and its enormous therapeutic potential for
a broad spectrum of diseases will be better exploited.
Each author has participated suciently in the work to take
public responsibility for appropriate portions of the content.
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Conict of Interest Statement:e authors declare that the research was con-
ducted in the absence of any commercial or nancial relationships that could be
construed as a potential conict of interest.
Copyright © 2017 Zhao, Bo, Kang and Li. is is an open-access article distributed
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... A high extracellular ATP (eATP) concentration constitutes a dangerassociated molecular pattern, triggering purinergic receptors and inducing inflammatory responses. 17 Activation of ATP receptors increases the secretion of interleukin (IL)-1β, IL-18 and IL-12, as well as the expression of MHC-II and costimulatory molecules (CD80, CD86, CD83) on antigen presenting cells, supporting T cell activation and a Th1 proliferation. 18 ATP stimulation also increases proliferation, production and promotes cytotoxicity of CD8 T cells. ...
... 18 ATP stimulation also increases proliferation, production and promotes cytotoxicity of CD8 T cells. 17 Hence, eATP is an integral part of the antitumour immune reaction. ...
... These processes culminate in T cell anergy. [17][18][19][20] Hence, accumulation of adenosine in the tumour microenvironment favours immune escape. We hypothesise that blocking CD39 enzymatic activity could abrogate adenosine accumulation and promote immune responses, making it a promising antitumour target in CRC. ...
Objective: T cells are major effectors of the antitumoural immune response. Their activation by tumour-associated antigens can unleash their proliferation and cytotoxic functions, leading to tumour cell elimination. However, tumour-related immunosuppressive mechanisms including the overexpression of immune checkpoints like programmed cell death protein-1 (PD-1), are also engaged, promoting immune escape. Current immunotherapies targeting these pathways have demonstrated weak efficacy in colorectal cancer (CRC). It is thus crucial to find new targets for immunotherapy in this cancer type. Design: In a prospective cohort of patients with CRC, we investigated the phenotype of tumour-related and non-tumour related intestinal T cells (n=44), particularly the adenosinergic pathway, correlating with clinical phenotype. An autologous coculture model was developed between patient-derived primary tumour spheroids and their autologous tumour-associated lymphocytes. We used this relevant model to assess the effects of CD39 blockade on the antitumour T cell response. Results: We show the increased expression of CD39, and its co-expression with PD-1, on tumour infiltrating T cells compared with mucosal lymphocytes. CD39 expression was higher in the right colon and early-stage tumours, thus defining a subset of patients potentially responsive to CD39 blockade. Finally, we demonstrate in autologous conditions that CD39 blockade triggers T cell infiltration and tumour spheroid destruction in cocultures. Conclusion: In CRC, CD39 is strongly expressed on tumour infiltrating lymphocytes and its inhibition represents a promising therapeutic strategy for treating patients.
... Purinergic signaling is an important mechanism in fine tuning immune cell functions (1)(2)(3). Extracellular ATP, released by damaged and dying cells, is a danger signal that plays a proinflammatory function. In T cell differentiation, ATP is secreted by activated T cells and stimulates P2X receptors (P2RX) (4). ...
... In addition, extracellular AMP produced by CD39 in the absence of CD73 is also immunosuppressive through binding to P1 receptors (7). Taken together, CD39 expression on the cell surface largely determines whether the microenvironment is proinflammatory or immunoregulatory (1)(2)(3). ...
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The ectonucleotidase CD39 functions as a checkpoint in purinergic signaling on effector T cells. By depleting eATP and initiating the generation of adenosine, it impairs memory cell development and contributes to T cell exhaustion, thereby causing defective tumor immunity and deficient T cell responses in older adults who have increased CD39 expression. Tuning enzymatic activity of CD39 and targeting the transcriptional regulation of ENTPD1 can be used to modulate purinergic signaling. Here, we describe that STAT6 phosphorylation downstream of IL-4 signaling represses CD39 expression on activated T cells by inducing a transcription factor network including GATA3, GFI1, and YY1. GATA3 suppresses ENTPD1 transcription through prevention of RUNX3 recruitment to the ENTPD1 promoter. Conversely, pharmacological STAT6 inhibition decreases T cell effector functions via increased CD39 expression, resulting in the defective signaling of P2X receptors by ATP and stimulation of A2A receptors by adenosine. Our studies suggest that inhibiting the STAT6 pathway to increase CD39 expression has the potential to treat autoimmune disease while stimulation of the pathway could improve T cell immunity.
... After activation, aged CD8 + T cells are also twice more likely than their younger counterparts to express CD39 [167]. CD39 works as a rate-liming ATPase by cleaving secreted ATP to generate adenosine [168]. Adenosine signals via the adenosine A2AR receptor to induce immune suppression and promote effector T cell apoptosis after antigen encounter, which impairs the memory T cell formation [169]. ...
... p < 0.05 was considered as statistically significant (Healthy pregnant group, n = 25, PE women, n = 25) and consequence changing of AMP to adenosine via CD39 and CD73 activities notify critical role of these enzymes in calibrating duration, magnitude, and particularity of purinergic signals. It is necessary to note that CD39 acts as rate-controling enzyme in ATP/CD39/CD73/adenosine cascade [31]. ...
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Background The Preeclampsia (PE) molecular mechanisms are not fully revealed and different biological processes are involved in the pathogenesis of PE. We aimed to evaluate adenosine and hypoxia-related signaling molecules in PE patients in the current study.Methods Decidua tissue and peripheral blood samples were taken from 25 healthy pregnant and 25 PE women at delivery time. CD39, CD73, and Hypoxia-inducible factor-alpha (HIF-α) were evaluated in mRNA and protein level using real-time PCR and western blotting techniques, respectively. Also, miR-30a, miR-206, and miR-18a expression were evaluated by real-time PCR. At last, secretion levels of IGF and TGF-β in the taken serum of blood samples were measured by ELISA.ResultsOur results revealed that Expression of CD39 is decreased in PE cases versus healthy controls at mRNA and protein levels (p = 0.0003 for both). CD73 and HIF-α showed an increased level of expression in PE patients at RNA and protein status (p = 0.0157 and p < 0.0001 for protein evaluation of CD73 and HIF-α, respectively). The miRNA-30a (p = 0.0037) and miR-206 (p = 0.0113) showed elevated expression in the decidua of the PE group. The concentration of secreted IGF-1 (p = 0.0002) and TGF-β (p = 0.0101) in serum samples of PE cases compared to the healthy group were decreased.Conclusion In conclusion, our results showed that aberrant expression of molecules that are involved in ATP catabolism and the hypoxic conditions is observed in PE cases and involved in their hypertension and inflammation could be served as PE prognosis by more confirming in comprehensive future studies.Graphical abstractmiR-206 and miR-30a play a role by regulating CD39 and CD73 as molecules that are involved in ATP catabolism as well as regulating the production of IGF-1 in the process of hypertension, which is the main feature in patients with preeclampsia. On the other hand, decreased level of miR-18a lead to upregulation of HIF-1a, and the consequence condition of hypoxia increases hypertension and inflammation in these patients.
... The frequencies of these subsets were altered in CLL patients compared to healthy donor controls. CD39 is expressed on exhausted CD8 + T cells and mediates suppressive activity in Tregs (80,81). CD39 + CCR7 + Tregs were identified in CLL patients that were not found in healthy donors, indicating a memory Treg subset with high suppressive capacity (79). ...
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Regulatory T cells (Tregs) are responsible for maintaining immune homeostasis by controlling immune responses. They can be characterized by concomitant expression of FoxP3, CD25 and inhibitory receptors such as PD-1 and CTLA-4. Tregs are key players in preventing autoimmunity and are dysregulated in cancer, where they facilitate tumor immune escape. B-cell lymphoid malignancies are a group of diseases with heterogenous molecular characteristics and clinical course. Treg levels are increased in patients with B-cell lymphoid malignancies and correlate with clinical outcomes. In this review, we discuss studies investigating Treg immunobiology in B-cell lymphoid malignancies, focusing on clinical correlations, mechanisms of accumulation, phenotype, and function. Overarching trends suggest that Tregs can be induced directly by tumor cells and recruited to the tumor microenvironment where they suppress antitumor immunity to facilitate disease progression. Further, we highlight studies showing that Tregs can be modulated by novel therapeutic agents such as immune checkpoint blockade and targeted therapies. Treg disruption by novel therapeutics may beneficially restore immune competence but has been associated with occurrence of adverse events. Strategies to achieve balance between these two outcomes will be paramount in the future to improve therapeutic efficacy and safety.
... Innate and acquired responses are participants of a highly regulated immune response in pregnancy [6,8]. CD39 and CD73 are ectoenzymes that sequentially metabolize ATP to adenosine, leading to an anti-inflammatory response [27,32]. Dorneles et al. showed a higher percentage of CD4+CD39+ cells in severe COVID-19 patients than in healthy controls and a lower percentage of CD4+CD73+ cells than in controls [30], suggesting that this could be a useful marker to follow progression in the general population with COVID-19. ...
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Current medical guidelines consider pregnant women with COVID-19 to be a high-risk group. Since physiological gestation downregulates the immunological response to maintain “maternal-fetal tolerance”, SARS-CoV-2 infection may constitute a potentially threatening condition to both the mother and the fetus. To establish the immune profile in pregnant COVID-19+ patients, a cross-sectional study was conducted. Pregnant women with COVID-19 (P-COVID-19+; n = 15) were analyzed and compared with nonpregnant women with COVID-19 (NP-COVID-19+; n = 15) or those with physiological pregnancy (P-COVID-19-; n = 13). Serological cytokine and chemokine concentrations, leucocyte immunophenotypes, and mononuclear leucocyte responses to polyclonal stimuli were analyzed in all groups. Higher concentrations of serological TNF-α, IL-6, MIP1b and IL-4 were observed within the P-COVID-19+ group, while cytokines and chemokines secreted by peripheral leucocytes in response to LPS, IL-6 or PMA-ionomicin were similar among the groups. Immunophenotype analysis showed a lower percentage of HLA-DR+ monocytes in P-COVID-19+ than in P-COVID-19- and a higher percentage of CD39+ monocytes in P-COVID-19+ than in NP-COVID-19+. After whole blood polyclonal stimulation, similar percentages of T cells and TNF+ monocytes between groups were observed. Our results suggest that P-COVID-19+ elicits a strong inflammatory response similar to NP-COVID19+ but also displays an anti-inflammatory response that controls the ATP/adenosine balance and prevents hyperinflammatory damage in COVID-19.
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CD39 (ENTPD1 - ectonucleoside triphosphate diphosphohydrolase 1) is a membrane-tethered ectonucleotidase that hydrolyzes extracellular ATP to ADP and ADP to AMP. This enzyme is expressed in a variety of cell types and tissues and has broadly been recognized within vascular tissue to have a protective role in converting “danger” ligands (ATP) into neutral or “protective” ligands (AMP, adenosine). In this study, we investigate the enzyme kinetics of CD39 using a Michaelis-Menten modeling framework. We show how the unique situation of having a reaction product also serving as a substrate (ADP) complicates the determination of the governing kinetic parameters. Model simulations using values for the kinetic parameters reported in the literature do not align with corresponding time-series data. This dissonance is explained by CD39 kinetic parameters previously being determined by graphical/linearization methods, which have been shown to distort the underlying error structure and lead to inaccurate parameter estimates. Modern methods of estimating these kinetic parameters using non-linear least squares is still challenging due to unidentifiable parameter interactions. We propose a workflow to accurately determine these parameters by isolating the ADPase and ATPase reactions and estimating the respective ADPase parameters and ATPase parameters with independent data sets. Theoretically, this ensures all kinetic parameters are identifiable and reliable for future prospective model simulations involving CD39. These kinds of mathematical models can be used to understand how circulating purinergic nucleotides affect disease etiology and potentially inform the development of corresponding therapies.
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CD47 is ubiquitously expressed on the surface of cells and plays a critical role in self-recognition. By interacting with SIRPα, TSP-1 and integrins, CD47 modulates cellular phagocytosis by macrophages, determines life span of individual erythrocytes, regulates activation of immune cells, and manipulates synaptic pruning during neuronal development. As such, CD47 has recently be regarded as one of novel innate checkpoint receptor targets for cancer immunotherapy. In this review, we will discuss increasing awareness about the diverse functions of CD47 and its role in immune system homeostasis. Then, we will discuss its potential therapeutic roles against cancer and outlines, the possible future research directions of CD47- based therapeutics against cancer.
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Single-cell technologies (RNA-sequencing, flow cytometry) are critical tools to reveal how cell heterogeneity impacts developmental pathways. The placenta is a fetal exchange organ, containing a heterogeneous mix of mesenchymal cells (fibroblasts, myofibroblasts, perivascular, and progenitor cells) . Placental mesenchymal stromal cells (pMSC) are also routinely isolated, for therapeutic and research purposes. However, our understanding of the diverse phenotypes of placental mesenchymal lineages, and their relationships remain unclear. We designed a 23-colour flow cytometry panel to assess mesenchymal heterogeneity in first-trimester human placentae. . Four distinct mesenchymal subsets were identified; CD73 ⁺ CD90 ⁺ mesenchymal cells, CD146 ⁺ CD271 ⁺ perivascular cells, podoplanin ⁺ CD36 ⁺ stromal cells, and CD26 ⁺ CD90 ⁺ myofibroblasts. CD73 ⁺ CD90 ⁺ and podoplanin+CD36+ cells expressed markers consistent with cultured pMSCs, and were explored further. Despite their distinct ex-vivo phenotype, in culture CD73 ⁺ CD90 ⁺ cells and podoplanin ⁺ CD36 ⁺ cells underwent phenotypic convergence, losing CD271 or CD36 expression respectively, and homogenously exhibiting a basic MSC phenotype (CD73 ⁺ CD90 ⁺ CD31 ⁻ CD144 ⁻ CD45 ⁻ ). However, some markers (CD26, CD146) were not impacted, or differentially impacted by culture in different populations. Comparisons of cultured phenotypes to pMSCs further suggested cultured pMSCs originate from podoplanin ⁺ CD36 ⁺ cells. This highlights the importance of detailed cell phenotyping to optimise therapeutic capacity, and ensure use of relevant cells in functional assays.
Colorectal cancer is one of the major concerns in both developed and developing societies. Because of the serious side effects of the current treatments, novel therapy agents have been developed that target immune checkpoint and immunomodulatory molecules in the tumor environment. Therefore, this study investigates the effect of docosahexaenoic acid (DHA) fatty acid on the expression of immune checkpoint molecule, PD‐L1, and immunomodulatory molecules, CD47 and CD39, and their controlling miRNAs in the colorectal cancer cell lines. Human colorectal cell lines HT‐29 and Caco‐2 were treated with 100 μM DHA and 50 μM LA for 24 h under the normoxic and hypoxic conditions. Total RNA was extracted and the qRT‐PCR was performed to analyze the expression of the studied genes and miRNAs. The western blotting technique was also used for validation. The qRT‐PCR results showed that DHA treatment increases the expression of the PD‐L1, CD47, and CD39 genes, but decreases these genes controlling miRNAs, mir‐424, mir‐133a, and mir‐142, respectively. Western blotting analysis demonstrated that PD‐L1 protein expression decreased after DHA treatment. LA administration had no inhibitory effect on the studied genes. This study showed that DHA has anti‐proliferative and anti‐metastatic properties by downregulation of proteins involved in the growth and invasion of colorectal tumors. DHA could be used as a potential immune checkpoint inhibitor for the treatment of colorectal cancers.
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The cytokine IL-22 plays a critical role in mucosal barrier defense, but the mechanisms that promote IL-22 expression in the human intestine remain poorly understood. As human microbe-responsive Vγ9/Vδ2 T cells are abundant in the gut and recognize microbiota-associated metabolites, we assessed their potential to induce IL-22 expression by intestinal CD4(+) T cells. Vγ9/Vδ2 T cells with characteristics of APCs were generated from human blood and intestinal organ cultures, then cocultured with naive and memory CD4(+) T cells obtained from human blood or the colon. The potency of blood and intestinal γδ T-APCs was compared with that of monocytes and dendritic cells, by assessing CD4(+) T cell phenotypes and proliferation as well as cytokine and transcription factor profiles. Vγ9/Vδ2 T cells in human blood, colon, and terminal ileum acquired APC functions upon microbial activation in the presence of microenvironmental signals including IL-15, and were capable of polarizing both blood and colonic CD4(+) T cells toward distinct effector fates. Unlike monocytes or dendritic cells, gut-homing γδ T-APCs employed an IL-6 independent mechanism to stimulate CD4(+) T cell expression of IL-22 without upregulating IL-17. In human intestinal organ cultures, microbial activation of Vγ9/Vδ2 T cells promoted mucosal secretion of IL-22 and ICOSL/TNF-α-dependent release of the IL-22 inducible antimicrobial protein calprotectin without modulating IL-17 expression. In conclusion, human γδ T-APCs stimulate CD4(+) T cell responses distinct from those induced by myeloid APCs to promote local barrier defense via mucosal release of IL-22 and calprotectin. Targeting of γδ T-APC functions may lead to the development of novel gut-directed immunotherapies and vaccines.
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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.
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Tumor microenvironment promotes immune suppression through recruiting and expanding suppressive immune cells such as regulatory T cells (Tregs) to facilitate cancer progression. In this study, we identify a novel CD39⁺ γδTreg in human colorectal cancer (CRC). CD39⁺ γδTregs are the predominant regulatory T cells and have more potent immunosuppressive activity than CD4⁺ or CD8⁺ Tregs via the adenosine-mediated pathway but independent of TGF-β or IL-10. They also secrete cytokines including IL-17A and GM-CSF which may chemoattract myeloid-derived suppressive cells (MDSCs) thus establishing an immunosuppressive network. We further demonstrate that tumor-derived TGF-β1 induces CD39⁺ γδT cells from paired normal colon tissues to produce more adenosine and become potent immunosuppressive T cells. Moreover, CD39⁺ γδTreg infiltration is positively correlated with TNM stage and other unfavorable clinicopathological features, implicating CD39⁺ γδTregs are one of the key players in establishment of immunosuppressive tumor microenvironment in human CRC that may be critical for tumor immunotherapy.
After a century of research, several lines of evidence now indicate that the ability of adenosine to directly control inflammatory cells has a major impact on the functions of the inflammatory and immune systems. Consequently, many promising therapeutic approaches are beginning to emerge that focus on the modulation of adenosine, including the development of compounds that interfere with the breakdown of adenosine, as well as specific agonists and antagonists of various adenosine subtypes. Some of these compounds have already entered clinical trials. While information on the role of adenosine is growing rapidly, until now it has remained scattered in the literature. Edited by three pioneering researchers in the field, Adenosine Receptors: Therapeutic Aspects for Inflammatory and Immune Diseases presents the first single volume compilation of reviews on how adenosine, acting on its cellular receptors, regulates immune responses. The book is organized to provide the reader with a general overview of adenosine receptors, delving into molecular biology, cell biology, and pharmacology. Separate chapters focus on the role of adenosine receptors in regulating the function of the various cell types that are involved in immune responses. Further chapters delineate the role of purinergic signaling in the pathophysiology of a variety of disease states associated with an overzealous or insufficient immune response. These include autoimmune diseases, asthma, atherosclerosis, ischemia-reperfusion injury, and cancer. Much of the methodology and findings documented in this text may well lead to new therapeutic modalities for pathologies such as ischemia and reperfusion, heart disease, wound healing, tumors, pain, and a variety of central nervous system diseases including Parkinson’s, Alzheimer’s, and epilepsy, as well as mood and sleep disorders. This resource provides background and direction for those researchers entering the field of adenosine and inflammatory disease, and provides a comprehensive reference for experienced investigators.
Human CD4⁺ T regulatory cells (Tregs) are a population of phenotypically and functionally diverse cells that downregulate inflammatory and autoimmune responses. As Th17 cells play an important role in the pathogenesis of autoimmune diseases, it is critical to elucidate the mechanisms regulating these cells. In this study, we examined the molecular basis underlying the phenotypic and functional diversity of human Tregs expressing the ectonucleotidase CD39. CD4⁺CD25hiCD39⁺ Tregs inhibit the proliferative response and the secretion of IL-17 and IFN-γ of autologous CD4⁺ T effector cells, while CD4⁺CD25hiCD39⁻ Tregs only suppress IFN-γ production. We demonstrate that activated human CD4⁺CD25hiCD39⁺ Tregs express the Th17-associated surface markers CCR6 and IL-23R, and phosphorylate the transcription factor Stat3. Moreover, suppression of IL-17 by CD4⁺CD25hiCD39⁺ Tregs occurs via a Stat3-dependent mechanism as inhibition of Stat3 activation in the CD39⁺ Tregs reverses their ability to suppress IL-17. CD4⁺CD25hiCD39⁻ Tregs are not endowed with the ability to inhibit IL-17 as they do not upregulate CCR6 or the IL-23R, and furthermore, they secrete IL-17. Our findings provide the first evidence that human Treg functional diversity is matched to the type of immune response being regulated and reveal a new role for Stat3 in controlling Treg function.
The exposition to traumatic events related to urban violence is epidemic in Brazil, with rate of 80% in the general population, and is becoming a major cause of post-traumatic stress disorder (PTSD). The objective of the study was to compare serum levels of pro-inflammatory interleukin-6 (IL-6) and anti-inflammatory interleukin-10 (IL-10) in PTSD and resilient individuals. We hypothesized that resilient individuals present an attenuated pro-inflammatory and enhanced anti-inflammatory state. We conducted a case-control study comparing 30 resilient individuals and 30 PTSD patients exposed to traumatic events related to urban violence. The groups were evaluated using Self-Report Questionnaire (SRQ-20), Mini-International Neuropsychiatric Interview (MINI) and the Davidson Trauma Scale. For all individuals, blood samples were collected to determine IL-6, IL-10 and cortisol serum levels. All samples were frozen at –80 °C until the assay and were analyzed with the same immunoassay kit and in duplicates. The resilient group presented higher IL-10 levels than PTSD patients [mean (CI); 1.03 (0.52–2.08) pg/mL vs. 0.29 (0.20–0.43) pg/mL; P = 0.002]. There were no differences in terms of IL-6 or cortisol levels. The results provided evidence for increased levels of IL-10 in resilient individuals when compared to PTSD patients, probably conferring them a better anti-inflammatory response after exposition.
Aim: This study aimed to identify CD4(+) T-cell-derived microparticles (MPs) and investigate their roles in rheumatoid arthritis (RA). Methods: Synovial fluids from 34 RA, 33 osteoarthritis patients and 42 healthy individuals were analyzed by flow cytometry. Human fibroblast-like synoviocytes and peripheral blood mononuclear cells were cultured with or without isolated MPs, chemokines and cytokines were measured by ELISA. Results: CD4(+)CD161(+)CD39(+) and CD4(+)CD39(+)CD73(+) MPs were abundantly present in RA patients, which were positively or negatively correlated with RA features, respectively. Chemokines CCL20, CCL17 and CCL22, and cytokines IL-17 and IL-10 were influenced by these MPs in human fibroblast-like synoviocytes (HFLS) or PMBCs. Conclusion: CD4(+) T-cell-derived CD161(+)CD39(+) and CD39(+)CD73(+) MPs could serve as new reciprocal biomarkers for RA evaluation.
Extracellular adenosine 5′-triphosphate (ATP) and adenosine molecules are intimately involved in immune responses. ATP is mostly a pro-inflammatory molecule and is released during hypoxic condition and by necrotic cells, as well as by activated immune cells and endothelial cells. However, under certain conditions, for instance at low concentrations or at prolonged exposure, ATP may also have anti-inflammatory properties. Extracellular ATP can activate both P2X and P2Y purinergic receptors. Extracellular ATP can be hydrolyzed into adenosine in a two-step enzymatic process involving the ectonucleotidases CD39 (ecto-apyrase) and CD73. These enzymes are expressed by many cell types, including endothelial cells and immune cells. The counterpart of ATP is adenosine, which is produced by breakdown of intra- or extracellular ATP. Adenosine has mainly anti-inflammatory effects by binding to the adenosine, or P1, receptors (A1, A2A, A2B, and A3). These receptors are also expressed in many cells, including immune cells. The final effect of ATP and adenosine in immune responses depends on the fine regulatory balance between the 2 molecules. In the present review, we will discuss the current knowledge on the role of these 2 molecules in the immune responses.