CD4⁺ regulatory T cells (Tregs), accounting for approximately 5–10% of total circulating CD4⁺ T cells, represent a critical subset of T lymphocytes involved in immune homeostasis. Through a broad set of effector mechanisms, these cells contribute to immune tolerance to self-constituents and to mucosal antigens derived from the commensal microflora and food (Lu et al., 2017; Xing and Hogquist, 2012). Tregs also participate in the resolution of inflammatory responses (Dominguez-Villar and Hafler, 2018) and play an important role in maternal immunotolerance against the semi-allogeneic fetus (Samstein et al., 2012). While critical to maintain tissue integrity, excessive activation of Tregs impedes adequate immune responses to tumors and pathogens, suggesting a tight control of their suppressive activity and tissue localization (Togashi et al., 2019; Aandahl et al., 2004; van der Burg et al., 2007). Although uniformly characterized by the expression of the lineage-specific, Foxp3 transcription factor (Lu et al., 2017), regulatory T cells display a wide range of phenotypic and functional properties that allow them to migrate to specific sites and suppress a variety of immune reactions, including inflammatory (Caridade et al., 2013) and humoral responses (Clement et al., 2019). Although diverse, the mechanisms whereby Tregs antagonize the activity of immune effectors are largely paracrine in nature (Vignali et al., 2008). Short-range suppressive mechanisms include competition for nutrients and/or growth factors (mostly cytokines), secretion of immunosuppressive factors, and direct, contact-mediated, inactivation of antigen-presenting cells (Wardell et al., 2021). These findings suggest that Tregs have to adapt to multiple lymphoid and nonlymphoid environments and suppress immune responses in a context and tissue-dependent fashion (Shevyrev and Tereshchenko, 2019; Panduro et al., 2016).

Oxygen represents an essential component of cellular bioenergetics and biochemistry. Because oxygen tension varies according to tissues and pathophysiological states (Ast and Mootha, 2019), cells need to adapt to fluctuations in oxygen availability in order to maintain an adequate functional and metabolic status. Of note, low-oxygen availability (hypoxia) plays a critical role in the pathophysiology of many immune disorders (McKeown, 2014; Bartels et al., 2013). Inflammation, in particular, is thought to reduce oxygen availability to tissues by affecting microvascular form and function, and through the recruitment of highly oxygen-consuming inflammatory cells producing NADPH oxidase-derived reactive oxygen species (Nanduri et al., 2015).

Immune cells patrolling through lymphoid and nonlymphoid tissues need therefore to readily adapt to varying oxygen concentration levels in order to exert their function (Mempel and Marangoni, 2019), suggesting an important role for oxygen sensors in immune regulation. Several hypoxia-sensitive pathways are known to enable single-cell survival in low-oxygen settings. In particular, reduced oxygen levels are directly sensed by a family of oxygen-dependent prolyl hydroxylases (PHD encoded by Egln gene, comprising three members) (Hirota, 2020), although other mechanisms mediated by oxygen-sensitive histone lysine demethylases (KDM) and the cysteamine dioxygenase/N-degron pathway have been recently uncovered (Baik and Jain, 2020). Hypoxia-inducible factors (HIFs), a set of evolutionary conserved transcriptional regulators, represent the best-described substrates of PHDs. These factors are heterodimers composed of a HIFα subunit whose stability is directly controlled by oxygen availability and a constitutively expressed HIF1β subunit (also known as ARNT) (Wang and Semenza, 1995). Following the initial characterization of the first member of HIFα family (HIF1α), two additional members, HIF2α and HIF3α, have been identified and shown to be similarly regulated by O₂ availability and bind to HIF1β (Webb et al., 2009). In normoxia, PHDs, whose affinity for oxygen is low and comparable to atmospheric concentrations, catalyze the prolyl-hydroxylation of HIFα subunits (Semenza, 2001). This post-translational modification allows recognition and ubiquitination of HIFα subunits by the E3 ubiquitin ligase Von Hippel–Lindau protein (pVHL) and subsequent degradation by the proteasome (Maxwell et al., 1999). In hypoxia, nonhydroxylated alpha subunits escape degradation and translocate to the nucleus where they bind to constitutively expressed and stable beta subunits to constitute an active heterodimer able to regulate gene expression. This process promotes transcriptional regulation of numerous genes, ultimately leading to increased oxygen supply (such as angiogenesis) and promotion of anaerobic metabolism (Downes et al., 2018).

Multiple levels of complexity of this major regulatory axis have been recently uncovered. As previously suggested, the presence of several members of the PHD and HIF families suggests specialized functions of PHD-HIF pairs during ontogeny and in selected tissues (Watts and Walmsley, 2019). In particular, while HIF1α appears as ubiquitously expressed in all metazoans, HIF2α represents a late acquisition of vertebrates, displaying a more restricted tissue expression pattern (Talks et al., 2000). Although these factors bind to similar sequence motifs (hypoxia response elements [HREs]) and regulate the expression of a shared set of genes, both HIF1α and HIF2α-specific gene targets have been identified in multiple tissues (Downes et al., 2018; Hu et al., 2007; Bono and Hirota, 2020). Further complexity in this pathway stems from the possible occurrence of additional, non-HIF-related, PHD substrates (Meneses and Wielockx, 2016; Mikhaylova et al., 2008; Chan et al., 2009; Romero-Ruiz et al., 2012; Huo et al., 2012; Xie et al., 2015; Lee et al., 2015b; Guo et al., 2016), a set of findings that however has not been confirmed in more rigorous in vitro settings using well-defined synthetic substrates (Cockman et al., 2019).

Hypoxia plays a dual role in inflammation and in the regulation of immune responses. In most settings, hypoxia promotes inflammation, while in some instances, such as in tumor sites, low oxygen levels generally cause unresponsiveness of immune effectors, thus favoring tumor growth. The often-opposing effects displayed by HIF activation on the activity of immune cells equally match this complexity (Corrado and Fontana, 2020). Previous work has indeed highlighted the important role of the PHD-HIF axis in regulating both innate and adaptive immune effectors (Watts and Walmsley, 2019). The role of HIF1α in regulating T cell activity has been described in many studies and is mainly linked to the capacity of this hypoxia-induced transcription factor to promote glycolysis (for a review, see McGettrick and O’Neill, 2020). Accordingly, HIF1α expression favors the development of highly glycolytic inflammatory Th17 cells, while inhibiting the development of Tregs, which rely mostly on aerobic metabolism (Shi et al., 2011). HIF1α also plays a direct role in Th17 development, through the transcriptional activation of Rorc (Dang et al., 2011). The role of HIF1α in Th1 development appears as more complex and context-dependent. Hypoxia decreases IFN-γ production of Th1-like cells in a HIF1α-dependent fashion (Shehade et al., 2015), while sustained expression of this transcription factor in normoxia (as observed in mice lacking PHDs expression; Clever et al., 2016) leads to an increase in IFN-γ-secreting CD4⁺ T cells. Of note, expression of HIF1α can be upregulated in normoxia both by TCR (Lukashev et al., 2001) and cytokine-initiated signals (Dang et al., 2011), confirming that HIF1α may play a role in Th1 cells development both in hypoxia and normoxia.

The role of hypoxia-induced factors in Treg development and function is presently not fully elucidated. As previously discussed, HIF1α deficiency improves Treg cell development, possibly a consequence of the limited requirement for glycolysis of this cell subset (Shi et al., 2011). However, hypoxia promotes Foxp3 expression in a HIF1α-dependent fashion (Ben-Shoshan et al., 2008) and expression of HIF1α is required for adequate regulatory T cell function (Clambey et al., 2012). Similarly, a recent report has identified HIF2α as an important mediator of Treg function in vivo, further stressing the important role of these hypoxia-induced factors in the control of in vivo inflammatory manifestations (Hsu et al., 2020). In agreement with these conclusions, PHD proteins have also been shown to play a role in the differentiation of peripheral (but not thymic-derived) Tregs (Clever et al., 2016). Expression of these proteins appears to redundantly regulate Th1 vs. iTreg development, mostly by limiting the accumulation of HIF1α. In contrast to this study, a recent publication has highlighted a selective role of the PHD2 isoform in the regulation of Treg function (Yamamoto et al., 2019). ShRNA-mediated knockdown of PHD2 expression in Foxp3-expressing cells (PHD2-KD Tregs) led to a systemic inflammatory syndrome characterized by mononuclear cell infiltration in several organs. PHD2-KD Tregs displayed reduced suppressive capacities both in vitro and in vivo, suggesting an important and intrinsic role of PHD2 in this cell subset. Of interest, loss of HIF2α expression reversed the phenotype of these mice bearing PHD2-KD Tregs, suggesting an important role of the PHD2-HIF2α axis in regulating Treg function.

To better delineate the role of PHD2, HIF1α, and HIF2α in the regulation of Treg development and function, we have generated a set of conditional mouse strains lacking expression of these hypoxia-responsive proteins in Foxp3⁺ cells. Using these tools, we confirm herein that mice in which expression of PHD2 is selectively inactivated in regulatory T cells display a spontaneous inflammatory syndrome characterized by altered immune homeostasis at the steady state and high sensitivity to Th1-type inflammatory diseases. This proinflammatory phenotype was accentuated by the concomitant loss of PHD2 and HIF1α, but almost completely alleviated in mice dually deficient for PHD2 and HIF2α. Transcriptome analysis confirmed a marginal role for HIF1α-dependent enhanced glycolysis in the regulation of Treg function and allowed us to identify STAT1 as a potential target of the PHD2-HIF2α axis in maintaining immune homeostasis and preventing excessive Th1-mediated inflammation.

This study highlights the important role of the prolyl-hydroxylase PHD2 in the regulation of Treg development and function. Deletion of PHD2 in developing Tregs led to the accumulation of the subset of Treg precursor characterized by low expression of Foxp3 at the expenses of the mature Foxp3⁺CD25⁺ Treg population (Figure 2c). PHD2-deficient Tregs were nevertheless found in increased numbers in vivo at steady state (Figure 2a), albeit with an altered phenotype. In particular, the expression of molecules known to be associated with optimal suppressive activity (such as Foxp3, ICOS ,and CD25) (Lu et al., 2017; Fontenot et al., 2003; Redpath et al., 2013) was marginally decreased, while the expression of PD-1, a marker associated with altered functional activity of many immune cells including Tregs (Lowther et al., 2016; Tan et al., 2021), was augmented. Of note, other molecules known to play an important role in Treg function were expressed at optimal levels (cf. CTLA4 and IL-10).

Although we have not specifically addressed the role of PHD2 in thymic vs. peripherally induced Tregs, it is noteworthy that lack of PHD2 expression altered Treg thymic development without any major effect on the generation of iTreg in vitro, suggesting a more pronounced role of PHD2 on thymic vs. peripherally generated Tregs, although this conclusion should be strengthened by additional studies.

Mice selectively lacking PHD2 expression in Treg displayed a proinflammatory phenotype (with early manifestations of gastrointestinal tract inflammation) associated to an elevated hematocrit, enhanced vascular permeability, and an altered homeostatic profile of splenic conventional T cells. In marked contrast to WT Tregs, PHD2-deficient Tregs express relatively high levels of Vegfa transcripts (as established from RNA-seq analysis), a factor known to both increase vascular permeability (Bates, 2010) and induce erythropoietin (Epo) production from perivascular stromal cells in several organs (Greenwald et al., 2019). Alternatively, since the expression of the YFP-Cre allele was found in a minor proportion of CD45-negative cells in all organs examined (see Figure 8—figure supplement 1). PHD2 deletion could result in elevated expression of Epo from a nonhematopoietic source. In any event, analysis of several organs (including spleen, liver, and kidney) from PHD2^ΔTreg mice failed to reveal any increase in Epo mRNA accumulation (our own unpublished observations), and further studies will therefore be required to identify the mechanism underlying the observed hematological alterations in PHD2^ΔTreg mice. Several observations, however, strongly indicate that the major proinflammatory phenotype observed in these mice were due to the specific impairment in Treg function consequent to the loss of PHD2 activity. Despite previous reports describing the stochastic activity of the Foxp3-Cre-YFP allele in non-Tregs leading to the recombination of some, but not all, alleles (Franckaert et al., 2015), we consistently found a control-level expression of PHD2 in all conventional T cell subsets tested (Figure 1—figure supplement 1). Secondly, co-transfer of highly purified Tregs with WT naive CD4⁺ conventional target cells clearly demonstrated an intrinsic role of PHD2 in regulating Treg function. Finally, and this will be discussed further below, mice bearing double PHD2-HIF2α-deficient Tregs recover a near-control phenotype, further excluding a major influence of the genetic background on the observed phenotype. Our observations confirm and further extend the observations from a study published during the completion of our work (Yamamoto et al., 2019), indicating a specific nonredundant role for PHD2 in controlling Treg activity in vivo.

Based on the notion that hypoxia-induced factors represent major substrates of PHD2, we generated a series of mouse strains to evaluate the relative role of HIF1α and HIF2α in regulating Treg phenotype and function. The combined loss of PHD2 and HIF2α, but not HIF1α, corrected some, but not all, abnormalities found in the PHD2^ΔTreg mouse strain. To uncover the mechanism whereby the PHD2-HIF2α axis regulates the capacity of Tregs to exert a homeostatic control over conventional T cells, a large transcriptomic analysis was undertaken. To be able to isolate genes specifically involved in the control of Treg activity in naive animals, we took advantage of the graded proinflammatory status of the mouse strain generated (based on colon length and spontaneous activation of Tconv cells, see Figure 6) to identify the gene clusters whose expression correlated with Treg-mediated immune homeostasis. This analysis led us to identify the important pathways providing mechanistic insights into the role of the PHD2-HIF2α axis in Treg biology. In particular, loss of PHD2 led to an altered expression of genes coding for chemokine receptors and adhesion molecules, suggesting a potential role of this oxygen sensor in chemotaxis and traffic. This conclusion is of particular interest in light of two observations described in this study. As previously discussed, PHD2^ΔTreg mice displayed a selective expansion of Th1-prone effectors in all lymphoid organs examined (Figure 1). Accordingly, ubiquitous loss of IFN-γ expression strongly attenuated the pro-inflammatory phenotype of mice with PHD2-deficient Tregs (Figure 5—figure supplement 2), thus suggesting a specific role for PHD2 in endowing Tregs to control Th1-like immune responses in vivo. Secondly, the IPA conducted on the transcriptomic data led to the identification of STAT1 as a potential common regulator of many genes whose expression was under the control of the PHD2-HIF2α axis, including in particular CXCR3 (Hall et al., 2012; Koch et al., 2009). Based on the well-described role for Treg-expressed CXCR3 in modulating Th1-like responses in vivo (Levine et al., 2017; Littringer et al., 2018) and the reduced expression of this chemokine receptor described in this study (Figure 8e), it is tempting to speculate that the reduced capacity of PHD2-deficient Tregs to control Th1 responses is a consequence of an altered STAT1 signaling pathway, leading to reduced CXCR3 expression. It is noteworthy that response to CXCR3 ligands has been recently shown to determine the precise positioning of effector and memory CD8 cells in peripheral lymph nodes (Duckworth et al., 2021). Further studies would be required to identify the precise mechanism at work since the expression of many potential chemokine receptors (including CXCR4, known to exert inhibitory function over other chemokine receptors; Biasci et al., 2020) and adhesion molecules (such as Ly6a or CD44) appears under the control of the PHD2-HIF2α axis in Tregs. Whether altered positioning of Tregs within lymphoid organs represents an important factor contributing to the proinflammatory phenotype of PHD2^ΔTreg mice remains, however, to be thoroughly examined. Similarly, the potential mechanistic link between HIF2α and STAT1 activation remains to be firmly established by further investigations.

Collectively, the observations reported in this study demonstrate a nonredundant role for PHD2 in controlling survival, phenotype, and the capacity of Tregs to control Th1-like responses. These biological responses appear under the control of HIF2α and are largely independent of HIF1α-regulated metabolic pathways. Although the role of the PHD2-HIF2α axis has been previously highlighted by Yamamoto and colleagues using an alternative shRNA-based approach (Yamamoto et al., 2019), our observations do not fully concur with the previous study on two grounds. First, in contrast to PHD2 knockdown (PHD2-KD) cells, PHD2-genetically deficient Tregs retained full suppressive capacities in vitro. Secondly, no sign of reversal to an effector state was found in PHD2-KO regulatory T cells, whereas downregulation of PHD2 expression led to an increased expression of T-bet, GATA-3, and TNFα. Notably, PHD2-KD Tregs were able to induce skin-graft rejection in the absence of bona fide effector cells, suggesting a possible acquisition of effector function by these cells. Although these observations are compatible with a possible gene-dosage effect of PHD2 on Treg biology, further studies are needed to identify the mechanism at work in these two experimental models.

In any events, both studies concur in identifying a possible deleterious role of HIF2α overactivation in the control of regulatory T cell function. These findings appear at odds with a recent publication by Tzu-Sheng Hsu and colleagues in which deletion of HIF2α, but not HIF1α, expression was found to negatively affect Treg function (Hsu et al., 2020). Of note, concomitant deletion of both HIF1α and HIF2α restored the suppressive activity of Tregs (Hsu et al., 2020). An elegant hypothesis, put forward by these authors, may help reconcile some of these apparently contradictory observations. Most experimental evidence concurs with a dual role of HIF1α in Treg differentiation and stability. In the setting of suboptimal Treg-inducing conditions, HIF1α may promote adequate expression of Foxp3 by differentiating Tregs. Once the Treg phenotype has been fully acquired, HIF1α protein expression is reduced following interaction with Foxp3 (Clambey et al., 2012), thus explaining the relative lack of influence of HIF1α on differentiated Tregs. As a consequence, HIF1α-KO Tregs retain full suppressive activity (Hsu et al., 2020). The interaction between HIF1α and Foxp3 can, however, also lead to Foxp3 protein degradation, and thus Treg instability. Therefore, forced stabilization of HIF1α (such as observed in triple PHD KOs [Clever et al., 2016] or pVHL-deficient Tregs [Lee et al., 2015a]) leads to loss of Foxp3 expression and Treg identity and acquisition of proinflammatory functions. Inflammation observed in these mouse strains can be largely attributed to the proinflammatory influence of ex-Tregs. As discussed for HIF1α, HIF2α also appears to regulate Treg stability, albeit in a different direction. Despite a normal phenotype at rest, mice displaying HIF2α-deficient Tregs were largely defective in suppressing inflammation in the gut and lungs (Hsu et al., 2020). This proinflammatory phenotype was largely explained by the HIF1α-dependent reprogramming of HIF2α-deficient Tregs into IL-17-secreting cells. Collectively, the available literature points to a central role for HIF1α in determining Treg stability and function in vivo. Depending on the biological pathway leading to its increased expression and/or protein stabilization, HIF1α promotes the differentiation of Tregs into IFN-γ (in triple PHD KOs or pVHL-deficient Tregs) or IL-17 (in HIF2α-deficient Tregs) secreting cells. Although the mechanism underlying the acquisition of Th1 vs. Th17-like profiles in these models remains to be established, the induction of a glycolytic metabolism is probably instrumental in mediating Treg instability (Shi and Chi, 2019).

In the present study, loss of HIF1α expression did not revert the phenotype of PHD2-HIF2α-deficient Tregs, despite re-establishing a control-like expression of pro-glycolytic genes (Figure 7e). Accordingly, PHD2-deficient Tregs did not acquire the capacity to produce proinflammatory cytokines (Figure 1—figure supplement 1) nor displayed any significant loss of Foxp3 expression upon in vitro culture (Figure 2k and l) or in vivo transfer (Figure 4e). Thus, the available evidence suggests that in PHD2-sufficient cells HIF2α allows adequate Treg function by negating the influence of HIF1α on Foxp3-expression, while overactivation of HIF2α activity secondary to the loss of PHD2 expression leads to altered Treg phenotype, most probably via a STAT1-dependent pathway.

Considering the specific role of PHD2, it is worth mentioning that both the transcriptomic data and our own unpublished observations (indicating an increased sensitivity of triple PHD2-HIF1α-HIF2α Tregs-specific KO mice to chemical induced colitis) suggest that while the capacity of Tregs to control tissue homeostasis in the naive state is under the predominant control of the PHD2-HIF2α axis, other non-HIF PHD2-substrates (Meneses and Wielockx, 2016; Mikhaylova et al., 2008; Chan et al., 2009; Romero-Ruiz et al., 2012; Huo et al., 2012; Xie et al., 2015; Lee et al., 2015b; Guo et al., 2016) probably play an important role in Treg biology under strong inflammatory settings. Finally, this study suggests that some caution should be exerted in the administration of PHD inhibitors presently considered for the treatment of renal anemia (Gupta and Wish, 2017), inflammatory bowel diseases (Marks et al., 2015), as well as Parkinson’s disease (Li et al., 2018) as these compounds may display some proinflammatory effects via the alteration of Treg phenotype and function in vivo.

Sequencing data have been deposited in GEO under accession code GSE184581. Numerical data used to generate the figures have been provided as source data files.

1. 1. Ajouaou Y
   2. Azouz A
   3. Taquin A
   4. Hussein H
   5. Andris F
   6. Moser M
   7. Goriely S
   8. Leo O

   (2021) NCBI Gene Expression Omnibus

   ID GSE184581. The oxygen sensor Prolyl hydroxylase domain 2 regulates the in vivo suppressive capacity of regulatory T cells.

   https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE184581

1. 1. Aandahl EM
   2. Michaëlsson J
   3. Moretto WJ
   4. Hecht FM
   5. Nixon DF

   (2004) Human CD4+ CD25+ regulatory T cells control T-cell responses to human immunodeficiency virus and cytomegalovirus antigens

   Journal of Virology 78:2454–2459.

   https://doi.org/10.1128/jvi.78.5.2454-2459.2004

   • PubMed
   • Google Scholar
2. 1. Ast T
   2. Mootha VK

   (2019) Oxygen and mammalian cell culture: are we repeating the experiment of Dr. Ox?

   Nature Metabolism 1:858–860.

   https://doi.org/10.1038/s42255-019-0105-0

   • PubMed
   • Google Scholar
3. 1. Baik AH
   2. Jain IH

   (2020) Turning the Oxygen Dial: Balancing the Highs and Lows

   Trends in Cell Biology 30:516–536.

   https://doi.org/10.1016/j.tcb.2020.04.005

   • PubMed
   • Google Scholar
4. 1. Bartels K
   2. Grenz A
   3. Eltzschig HK

   (2013) Hypoxia and inflammation are two sides of the same coin

   PNAS 110:18351–18352.

   https://doi.org/10.1073/pnas.1318345110

   • PubMed
   • Google Scholar
5. 1. Bates DO

   (2010) Vascular endothelial growth factors and vascular permeability

   Cardiovascular Research 87:262–271.

   https://doi.org/10.1093/cvr/cvq105

   • PubMed
   • Google Scholar
6. 1. Ben-Shoshan J
   2. Maysel-Auslender S
   3. Mor A
   4. Keren G
   5. George J

   (2008) Hypoxia controls CD4+CD25+ regulatory T-cell homeostasis via hypoxia-inducible factor-1alpha

   European Journal of Immunology 38:2412–2418.

   https://doi.org/10.1002/eji.200838318

   • PubMed
   • Google Scholar
7. 1. Biasci D
   2. Smoragiewicz M
   3. Connell CM
   4. Wang Z
   5. Gao Y
   6. Thaventhiran JED
   7. Basu B
   8. Magiera L
   9. Johnson TI
   10. Bax L
   11. Gopinathan A
   12. Isherwood C
   13. Gallagher FA
   14. Pawula M
   15. Hudecova I
   16. Gale D
   17. Rosenfeld N
   18. Barmpounakis P
   19. Popa EC
   20. Brais R
   21. Godfrey E
   22. Mir F
   23. Richards FM
   24. Fearon DT
   25. Janowitz T
   26. Jodrell DI

   (2020) CXCR4 inhibition in human pancreatic and colorectal cancers induces an integrated immune response

   PNAS 117:28960–28970.

   https://doi.org/10.1073/pnas.2013644117

   • PubMed
   • Google Scholar
8. 1. Bono H
   2. Hirota K

   (2020) Meta-Analysis of Hypoxic Transcriptomes from Public Databases

   Biomedicines 8:E10.

   https://doi.org/10.3390/biomedicines8010010

   • PubMed
   • Google Scholar
9. 1. Caridade M
   2. Graca L
   3. Ribeiro RM

   (2013) Mechanisms Underlying CD4+ Treg Immune Regulation in the Adult: From Experiments to Models

   Frontiers in Immunology 4:1–9.

   https://doi.org/10.3389/fimmu.2013.00378

   • PubMed
   • Google Scholar
10. 1. Chan DA
    2. Kawahara TLA
    3. Sutphin PD
    4. Chang HY
    5. Chi J-T
    6. Giaccia AJ

    (2009) Tumor vasculature is regulated by PHD2-mediated angiogenesis and bone marrow-derived cell recruitment

    Cancer Cell 15:527–538.

    https://doi.org/10.1016/j.ccr.2009.04.010

    • PubMed
    • Google Scholar
11. 1. Clambey ET
    2. McNamee EN
    3. Westrich JA
    4. Glover LE
    5. Campbell EL
    6. Jedlicka P
    7. de Zoeten EF
    8. Cambier JC
    9. Stenmark KR
    10. Colgan SP
    11. Eltzschig HK

    (2012) Hypoxia-inducible factor-1 alpha-dependent induction of FoxP3 drives regulatory T-cell abundance and function during inflammatory hypoxia of the mucosa

    PNAS 109:E2784–E2793.

    https://doi.org/10.1073/pnas.1202366109

    • PubMed
    • Google Scholar
12. 1. Clement RL
    2. Daccache J
    3. Mohammed MT
    4. Diallo A
    5. Blazar BR
    6. Kuchroo VK
    7. Lovitch SB
    8. Sharpe AH
    9. Sage PT

    (2019) Follicular regulatory T cells control humoral and allergic immunity by restraining early B cell responses

    Nature Immunology 20:1360–1371.

    https://doi.org/10.1038/s41590-019-0472-4

    • PubMed
    • Google Scholar
13. 1. Clever D
    2. Roychoudhuri R
    3. Constantinides MG
    4. Askenase MH
    5. Sukumar M
    6. Klebanoff CA
    7. Eil RL
    8. Hickman HD
    9. Yu Z
    10. Pan JH
    11. Palmer DC
    12. Phan AT
    13. Goulding J
    14. Gattinoni L
    15. Goldrath AW
    16. Belkaid Y
    17. Restifo NP

    (2016) Oxygen Sensing by T Cells Establishes an Immunologically Tolerant Metastatic Niche

    Cell 166:1117–1131.

    https://doi.org/10.1016/j.cell.2016.07.032

    • Google Scholar
14. 1. Cockman ME
    2. Lippl K
    3. Tian Y-M
    4. Pegg HB
    5. Figg WD
    6. Abboud MI
    7. Heilig R
    8. Fischer R
    9. Myllyharju J
    10. Schofield CJ
    11. Ratcliffe PJ

    (2019) Lack of activity of recombinant HIF prolyl hydroxylases (PHDs) on reported non-HIF substrates

    eLife 8:e46490.

    https://doi.org/10.7554/eLife.46490

    • PubMed
    • Google Scholar
15. 1. Corrado C
    2. Fontana S

    (2020) Hypoxia and HIF Signaling: One Axis with Divergent Effects

    International Journal of Molecular Sciences 21:1–17.

    https://doi.org/10.3390/ijms21165611

    • PubMed
    • Google Scholar
16. 1. Dang EV
    2. Barbi J
    3. Yang H-Y
    4. Jinasena D
    5. Yu H
    6. Zheng Y
    7. Bordman Z
    8. Fu J
    9. Kim Y
    10. Yen H-R
    11. Luo W
    12. Zeller K
    13. Shimoda L
    14. Topalian SL
    15. Semenza GL
    16. Dang CV
    17. Pardoll DM
    18. Pan F

    (2011) Control of T(H)17/T(reg) balance by hypoxia-inducible factor 1

    Cell 146:772–784.

    https://doi.org/10.1016/j.cell.2011.07.033

    • PubMed
    • Google Scholar
17. 1. Dominguez-Villar M
    2. Hafler DA

    (2018) Regulatory T cells in autoimmune disease

    Nature Immunology 19:665–673.

    https://doi.org/10.1038/s41590-018-0120-4

    • PubMed
    • Google Scholar
18. 1. Downes NL
    2. Laham-Karam N
    3. Kaikkonen MU
    4. Ylä-Herttuala S

    (2018) Differential but Complementary HIF1α and HIF2α Transcriptional Regulation

    Molecular Therapy 26:1735–1745.

    https://doi.org/10.1016/j.ymthe.2018.05.004

    • PubMed
    • Google Scholar
19. 1. Duckworth BC
    2. Lafouresse F
    3. Wimmer VC
    4. Broomfield BJ
    5. Dalit L
    6. Alexandre YO
    7. Sheikh AA
    8. Qin RZ
    9. Alvarado C
    10. Mielke LA
    11. Pellegrini M
    12. Mueller SN
    13. Boudier T
    14. Rogers KL
    15. Groom JR

    (2021) Effector and stem-like memory cell fates are imprinted in distinct lymph node niches directed by CXCR3 ligands

    Nature Immunology 22:434–448.

    https://doi.org/10.1038/s41590-021-00878-5

    • Google Scholar
20. 1. Esplugues E
    2. Huber S
    3. Gagliani N
    4. Hauser AE
    5. Town T
    6. Wan YY
    7. O’Connor W
    8. Rongvaux A
    9. Van Rooijen N
    10. Haberman AM
    11. Iwakura Y
    12. Kuchroo VK
    13. Kolls JK
    14. Bluestone JA
    15. Herold KC
    16. Flavell RA

    (2011) Control of TH17 cells occurs in the small intestine

    Nature 475:514–518.

    https://doi.org/10.1038/nature10228

    • Google Scholar
21. 1. Fontenot JD
    2. Gavin MA
    3. Rudensky AY

    (2003) Foxp3 programs the development and function of CD4+CD25+ regulatory T cells

    Nature Immunology 4:330–336.

    https://doi.org/10.1038/ni904

    • Google Scholar
22. 1. Franckaert D
    2. Dooley J
    3. Roos E
    4. Floess S
    5. Huehn J
    6. Luche H
    7. Fehling HJ
    8. Liston A
    9. Linterman MA
    10. Schlenner SM

    (2015) Promiscuous Foxp3-cre activity reveals a differential requirement for CD28 in Foxp3+ Promiscuous Foxp3-cre activity reveals a differential requirement for CD28 in Foxp3- Promiscuous Foxp3-cre activity reveals a differential requirement for CD28 in Foxp3

    Immunology and Cell Biology 93:417–423.

    https://doi.org/10.1038/icb.2014.108

    • PubMed
    • Google Scholar
23. 1. Greenwald AC
    2. Licht T
    3. Kumar S
    4. Oladipupo SS
    5. Iyer S
    6. Grunewald M
    7. Keshet E

    (2019) VEGF expands erythropoiesis via hypoxia-independent induction of erythropoietin in noncanonical perivascular stromal cells

    The Journal of Experimental Medicine 216:215–230.

    https://doi.org/10.1084/jem.20180752

    • PubMed
    • Google Scholar
24. 1. Guo J
    2. Chakraborty AA
    3. Liu P
    4. Gan W
    5. Zheng X
    6. Inuzuka H
    7. Wang B
    8. Zhang J
    9. Zhang L
    10. Yuan M
    11. Novak J
    12. Cheng JQ
    13. Toker A
    14. Signoretti S
    15. Zhang Q
    16. Asara JM
    17. Kaelin WG Jr
    18. Wei W

    (2016) pVHL suppresses kinase activity of Akt in a proline-hydroxylation-dependent manner

    Science (New York, N.Y.) 353:929–932.

    https://doi.org/10.1126/science.aad5755

    • PubMed
    • Google Scholar
25. 1. Gupta N
    2. Wish JB

    (2017) Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibitors: A Potential New Treatment for Anemia in Patients With CKD

    American Journal of Kidney Diseases 69:815–826.

    https://doi.org/10.1053/j.ajkd.2016.12.011

    • PubMed
    • Google Scholar
26. 1. Hall AO
    2. Beiting DP
    3. Tato C
    4. John B
    5. Oldenhove G
    6. Lombana CG
    7. Pritchard GH
    8. Silver JS
    9. Bouladoux N
    10. Stumhofer JS
    11. Harris TH
    12. Grainger J
    13. Wojno EDT
    14. Wagage S
    15. Roos DS
    16. Scott P
    17. Turka LA
    18. Cherry S
    19. Reiner SL
    20. Cua D
    21. Belkaid Y
    22. Elloso MM
    23. Hunter CA

    (2012) The cytokines interleukin 27 and interferon-γ promote distinct Treg cell populations required to limit infection-induced pathology

    Immunity 37:511–523.

    https://doi.org/10.1016/j.immuni.2012.06.014

    • PubMed
    • Google Scholar
27. 1. Hirota K

    (2020) Basic Biology of Hypoxic Responses Mediated by the Transcription Factor HIFs and its Implication for Medicine

    Biomedicines 8:E32.

    https://doi.org/10.3390/biomedicines8020032

    • PubMed
    • Google Scholar
28. 1. Hsu T-S
    2. Lin Y-L
    3. Wang Y-A
    4. Mo S-T
    5. Chi P-Y
    6. Lai AC-Y
    7. Pan H-Y
    8. Chang Y-J
    9. Lai M-Z

    (2020) HIF-2α is indispensable for regulatory T cell function

    Nature Communications 11:1–16.

    https://doi.org/10.1038/s41467-020-18731-y

    • PubMed
    • Google Scholar
29. 1. Hu CJ
    2. Sataur A
    3. Wang L
    4. Chen H
    5. Simon MC

    (2007) The N-terminal transactivation domain confers target gene specificity of hypoxia-inducible factors HIF-1alpha and HIF-2alpha

    Molecular Biology of the Cell 18:4528–4542.

    https://doi.org/10.1091/mbc.e06-05-0419

    • PubMed
    • Google Scholar
30. 1. Huo Z
    2. Ye J-C
    3. Chen J
    4. Lin X
    5. Zhou Z-N
    6. Xu X-R
    7. Li C-M
    8. Qi M
    9. Liang D
    10. Liu Y
    11. Li J

    (2012) Prolyl hydroxylase domain protein 2 regulates the intracellular cyclic AMP level in cardiomyocytes through its interaction with phosphodiesterase 4D

    Biochemical and Biophysical Research Communications 427:73–79.

    https://doi.org/10.1016/j.bbrc.2012.09.005

    • PubMed
    • Google Scholar
31. 1. Kim JJ
    2. Shajib MS
    3. Manocha MM
    4. Khan WI

    (2012) Investigating intestinal inflammation in DSS-induced model of IBD

    Journal of Visualized Experiments 1:1–6.

    https://doi.org/10.3791/3678

    • PubMed
    • Google Scholar
32. 1. Koch MA
    2. Tucker-Heard G
    3. Perdue NR
    4. Killebrew JR
    5. Urdahl KB
    6. Campbell DJ

    (2009) The transcription factor T-bet controls regulatory T cell homeostasis and function during type 1 inflammation

    Nature Immunology 10:595–602.

    https://doi.org/10.1038/ni.1731

    • PubMed
    • Google Scholar
33. 1. Lee JH
    2. Elly C
    3. Park Y
    4. Liu YC

    (2015a) E3 Ubiquitin Ligase VHL Regulates Hypoxia-Inducible Factor-1α to Maintain Regulatory T Cell Stability and Suppressive Capacity

    Immunity 42:1062–1074.

    https://doi.org/10.1016/j.immuni.2015.05.016

    • PubMed
    • Google Scholar
34. 1. Lee DC
    2. Sohn HA
    3. Park ZY
    4. Oh S
    5. Kang YK
    6. Lee KM
    7. Kang M
    8. Jang YJ
    9. Yang SJ
    10. Hong YK
    11. Noh H
    12. Kim JA
    13. Kim DJ
    14. Bae KH
    15. Kim DM
    16. Chung SJ
    17. Yoo HS
    18. Yu DY
    19. Park KC
    20. Yeom YI

    (2015b) A lactate-induced response to hypoxia

    Cell 161:595–609.

    https://doi.org/10.1016/j.cell.2015.03.011

    • PubMed
    • Google Scholar
35. 1. Levine AG
    2. Mendoza A
    3. Hemmers S
    4. Moltedo B
    5. Niec RE
    6. Schizas M
    7. Hoyos BE
    8. Putintseva EV
    9. Chaudhry A
    10. Dikiy S
    11. Fujisawa S
    12. Chudakov DM
    13. Treuting PM
    14. Rudensky AY

    (2017) Stability and function of regulatory T cells expressing the transcription factor T-bet

    Nature 546:421–425.

    https://doi.org/10.1038/nature22360

    • PubMed
    • Google Scholar
36. 1. Li X
    2. Cui XX
    3. Chen YJ
    4. Wu TT
    5. Xu H
    6. Yin H
    7. Wu YC

    (2018) Therapeutic Potential of a Prolyl Hydroxylase Inhibitor FG-4592 for Parkinson’s Diseases in Vitro and in Vivo: Regulation of Redox Biology and Mitochondrial Function

    Frontiers in Aging Neuroscience 10:1–16.

    https://doi.org/10.3389/fnagi.2018.00121

    • PubMed
    • Google Scholar
37. 1. Littringer K
    2. Moresi C
    3. Rakebrandt N
    4. Zhou X
    5. Schorer M
    6. Dolowschiak T
    7. Kirchner F
    8. Rost F
    9. Keller CW
    10. McHugh D
    11. LeibundGut-Landmann S
    12. Robinson MD
    13. Joller N

    (2018) Common Features of Regulatory T Cell Specialization During Th1 Responses

    Frontiers in Immunology 9:1–15.

    https://doi.org/10.3389/fimmu.2018.01344

    • Google Scholar
38. 1. Lowther DE
    2. Goods BA
    3. Lucca LE
    4. Lerner BA
    5. Raddassi K
    6. van Dijk D
    7. Hernandez AL
    8. Duan X
    9. Gunel M
    10. Coric V
    11. Krishnaswamy S
    12. Love JC
    13. Hafler DA

    (2016) PD-1 marks dysfunctional regulatory T cells in malignant gliomas

    JCI Insight 1:1–15.

    https://doi.org/10.1172/jci.insight.85935

    • PubMed
    • Google Scholar
39. 1. Lu L
    2. Barbi J
    3. Pan F

    (2017) The regulation of immune tolerance by FOXP3

    Nature Reviews. Immunology 17:703–717.

    https://doi.org/10.1038/nri.2017.75

    • PubMed
    • Google Scholar
40. 1. Lukashev D
    2. Caldwell C
    3. Ohta A
    4. Chen P
    5. Sitkovsky M

    (2001) Differential regulation of two alternatively spliced isoforms of hypoxia-inducible factor-1 alpha in activated T lymphocytes

    The Journal of Biological Chemistry 276:48754–48763.

    https://doi.org/10.1074/jbc.M104782200

    • PubMed
    • Google Scholar
41. 1. Marks E
    2. Goggins BJ
    3. Cardona J
    4. Cole S
    5. Minahan K
    6. Mateer S
    7. Walker MM
    8. Shalwitz R
    9. Keely S

    (2015) Oral delivery of prolyl hydroxylase inhibitor: AKB-4924 promotes localized mucosal healing in a mouse model of colitis

    Inflammatory Bowel Diseases 21:267–275.

    https://doi.org/10.1097/MIB.0000000000000277

    • PubMed
    • Google Scholar
42. 1. Maxwell PH
    2. Wiesener MS
    3. Chang GW
    4. Clifford SC
    5. Vaux EC
    6. Cockman ME
    7. Wykoff CC
    8. Pugh CW
    9. Maher ER
    10. Ratcliffe PJ

    (1999) The tumour suppressor protein VHL targets hypoxia-inducible factors for oxygen-dependent proteolysis

    Nature 399:271–275.

    https://doi.org/10.1038/20459

    • PubMed
    • Google Scholar
43. 1. McGettrick AF
    2. O’Neill LAJ

    (2020) The Role of HIF in Immunity and Inflammation

    Cell Metabolism 32:524–536.

    https://doi.org/10.1016/j.cmet.2020.08.002

    • PubMed
    • Google Scholar
44. 1. McKeown SR

    (2014) Defining normoxia, physoxia and hypoxia in tumours-implications for treatment response

    The British Journal of Radiology 87:1–12.

    https://doi.org/10.1259/bjr.20130676

    • PubMed
    • Google Scholar
45. 1. Mempel TR
    2. Marangoni F

    (2019) Guidance factors orchestrating regulatory T cell positioning in tissues during development, homeostasis, and response

    Immunological Reviews 289:129–141.

    https://doi.org/10.1111/imr.12761

    • PubMed
    • Google Scholar
46. 1. Meneses AM
    2. Wielockx B

    (2016) PHD2: from hypoxia regulation to disease progression

    Hypoxia (Auckland, N.Z.) 4:53–67.

    https://doi.org/10.2147/HP.S53576

    • PubMed
    • Google Scholar
47. 1. Mikhaylova O
    2. Ignacak ML
    3. Barankiewicz TJ
    4. Harbaugh SV
    5. Yi Y
    6. Maxwell PH
    7. Schneider M
    8. Van Geyte K
    9. Carmeliet P
    10. Revelo MP
    11. Wyder M
    12. Greis KD
    13. Meller J
    14. Czyzyk-Krzeska MF

    (2008) The von Hippel-Lindau tumor suppressor protein and Egl-9-Type proline hydroxylases regulate the large subunit of RNA polymerase II in response to oxidative stress

    Molecular and Cellular Biology 28:2701–2717.

    https://doi.org/10.1128/MCB.01231-07

    • PubMed
    • Google Scholar
48. 1. Nanduri J
    2. Vaddi DR
    3. Khan SA
    4. Wang N
    5. Makarenko V
    6. Semenza GL
    7. Prabhakar NR

    (2015) HIF-1α activation by intermittent hypoxia requires NADPH oxidase stimulation by xanthine oxidase

    PLOS ONE 10:e119762.

    https://doi.org/10.1371/journal.pone.0119762

    • PubMed
    • Google Scholar
49. 1. Owen DL
    2. Mahmud SA
    3. Sjaastad LE
    4. Williams JB
    5. Spanier JA
    6. Simeonov DR
    7. Ruscher R
    8. Huang W
    9. Proekt I
    10. Miller CN
    11. Hekim C
    12. Jeschke JC
    13. Aggarwal P
    14. Broeckel U
    15. LaRue RS
    16. Henzler CM
    17. Alegre M-L
    18. Anderson MS
    19. August A
    20. Marson A
    21. Zheng Y
    22. Williams CB
    23. Farrar MA

    (2019) Thymic regulatory T cells arise via two distinct developmental programs

    Nature Immunology 20:195–205.

    https://doi.org/10.1038/s41590-018-0289-6

    • PubMed
    • Google Scholar
50. 1. Panduro M
    2. Benoist C
    3. Mathis D

    (2016) Tissue Tregs

    Annual Review of Immunology 34:609–633.

    https://doi.org/10.1146/annurev-immunol-032712-095948

    • PubMed
    • Google Scholar
51. 1. Radu M
    2. Chernoff J

    (2013) An in vivo assay to test blood vessel permeability

    Journal of Visualized Experiments 1:e50062.

    https://doi.org/10.3791/50062

    • PubMed
    • Google Scholar
52. 1. Redpath SA
    2. van der Werf N
    3. Cervera AM
    4. MacDonald AS
    5. Gray D
    6. Maizels RM
    7. Taylor MD

    (2013) ICOS controls Foxp3(+) regulatory T-cell expansion, maintenance and IL-10 production during helminth infection

    European Journal of Immunology 43:705–715.

    https://doi.org/10.1002/eji.201242794

    • PubMed
    • Google Scholar
53. 1. Romero-Ruiz A
    2. Bautista L
    3. Navarro V
    4. Heras-Garvín A
    5. March-Díaz R
    6. Castellano A
    7. Gómez-Díaz R
    8. Castro MJ
    9. Berra E
    10. López-Barneo J
    11. Pascual A

    (2012) Prolyl hydroxylase-dependent modulation of eukaryotic elongation factor 2 activity and protein translation under acute hypoxia

    The Journal of Biological Chemistry 287:9651–9658.

    https://doi.org/10.1074/jbc.M111.299180

    • PubMed
    • Google Scholar
54. 1. Rubtsov YP
    2. Rasmussen JP
    3. Chi EY
    4. Fontenot J
    5. Castelli L
    6. Ye X
    7. Treuting P
    8. Siewe L
    9. Roers A
    10. Henderson WR Jr
    11. Muller W
    12. Rudensky AY

    (2008) Regulatory T cell-derived interleukin-10 limits inflammation at environmental interfaces

    Immunity 28:546–558.

    https://doi.org/10.1016/j.immuni.2008.02.017

    • PubMed
    • Google Scholar
55. 1. Samstein RM
    2. Josefowicz SZ
    3. Arvey A
    4. Treuting PM
    5. Rudensky AY

    (2012) Extrathymic generation of regulatory T cells in placental mammals mitigates maternal-fetal conflict

    Cell 150:29–38.

    https://doi.org/10.1016/j.cell.2012.05.031

    • PubMed
    • Google Scholar
56. 1. Semenza GLH

    (2001) HIF-1, O(2), and the 3 PHDs: how animal cells signal hypoxia to the nucleus

    Cell 107:1–3.

    https://doi.org/10.1016/s0092-8674(01)00518-9

    • PubMed
    • Google Scholar
57. 1. Shehade H
    2. Acolty V
    3. Moser M
    4. Oldenhove G

    (2015) Cutting Edge: Hypoxia-Inducible Factor 1 Negatively Regulates Th1 Function

    Journal of Immunology (Baltimore, Md 195:1372–1376.

    https://doi.org/10.4049/jimmunol.1402552

    • PubMed
    • Google Scholar
58. 1. Shevyrev D
    2. Tereshchenko V

    (2019) Treg Heterogeneity, Function, and Homeostasis

    Frontiers in Immunology 10:1–13.

    https://doi.org/10.3389/fimmu.2019.03100

    • PubMed
    • Google Scholar
59. 1. Shi LZ
    2. Wang R
    3. Huang G
    4. Vogel P
    5. Neale G
    6. Green DR
    7. Chi H

    (2011) HIF1alpha-dependent glycolytic pathway orchestrates a metabolic checkpoint for the differentiation of TH17 and Treg cells

    The Journal of Experimental Medicine 208:1367–1376.

    https://doi.org/10.1084/jem.20110278

    • PubMed
    • Google Scholar
60. 1. Shi H
    2. Chi H

    (2019) Metabolic Control of Treg Cell Stability, Plasticity, and Tissue-Specific Heterogeneity

    Frontiers in Immunology 10:1–17.

    https://doi.org/10.3389/fimmu.2019.02716

    • PubMed
    • Google Scholar
61. 1. Talks KL
    2. Turley H
    3. Gatter KC
    4. Maxwell PH
    5. Pugh CW
    6. Ratcliffe PJ
    7. Harris AL

    (2000) The expression and distribution of the hypoxia-inducible factors HIF-1alpha and HIF-2alpha in normal human tissues, cancers, and tumor-associated macrophages

    The American Journal of Pathology 157:411–421.

    https://doi.org/10.1016/s0002-9440(10)64554-3

    • PubMed
    • Google Scholar
62. 1. Tan CL
    2. Kuchroo JR
    3. Sage PT
    4. Liang D
    5. Francisco LM
    6. Buck J
    7. Thaker YR
    8. Zhang Q
    9. McArdel SL
    10. Juneja VR
    11. Lee SJ
    12. Lovitch SB
    13. Lian C
    14. Murphy GF
    15. Blazar BR
    16. Vignali DAA
    17. Freeman GJ
    18. Sharpe AH

    (2021) PD-1 restraint of regulatory T cell suppressive activity is critical for immune tolerance

    The Journal of Experimental Medicine 218:e20182232.

    https://doi.org/10.1084/jem.20182232

    • PubMed
    • Google Scholar
63. 1. Togashi Y
    2. Shitara K
    3. Nishikawa H

    (2019) Regulatory T cells in cancer immunosuppression - implications for anticancer therapy

    Nature Reviews. Clinical Oncology 16:356–371.

    https://doi.org/10.1038/s41571-019-0175-7

    • PubMed
    • Google Scholar
64. 1. van der Burg SH
    2. Piersma SJ
    3. de Jong A
    4. van der Hulst JM
    5. Kwappenberg KMC
    6. van den Hende M
    7. Welters MJP
    8. Van Rood JJ
    9. Fleuren GJ
    10. Melief CJM
    11. Kenter GG
    12. Offringa R

    (2007) Association of cervical cancer with the presence of CD4+ regulatory T cells specific for human papillomavirus antigens

    PNAS 104:12087–12092.

    https://doi.org/10.1073/pnas.0704672104

    • PubMed
    • Google Scholar
65. 1. Vignali DAA
    2. Collison LW
    3. Workman CJ

    (2008) How regulatory T cells work

    Nature Reviews. Immunology 8:523–532.

    https://doi.org/10.1038/nri2343

    • PubMed
    • Google Scholar
66. 1. Wang GL
    2. Semenza GL

    (1995) Purification and characterization of hypoxia-inducible factor 1

    The Journal of Biological Chemistry 270:1230–1237.

    https://doi.org/10.1074/jbc.270.3.1230

    • PubMed
    • Google Scholar
67. 1. Wardell CM
    2. MacDonald KN
    3. Levings MK
    4. Cook L

    (2021) Cross talk between human regulatory T cells and antigen-presenting cells: Lessons for clinical applications

    European Journal of Immunology 51:27–38.

    https://doi.org/10.1002/eji.202048746

    • PubMed
    • Google Scholar
68. 1. Watts ER
    2. Walmsley SR

    (2019) Inflammation and Hypoxia: HIF and PHD Isoform Selectivity

    Trends in Molecular Medicine 25:33–46.

    https://doi.org/10.1016/j.molmed.2018.10.006

    • PubMed
    • Google Scholar
69. 1. Webb JD
    2. Coleman ML
    3. Pugh CW

    (2009) Hypoxia, hypoxia-inducible factors (HIF), HIF hydroxylases and oxygen sensing

    Cellular and Molecular Life Sciences 66:3539–3554.

    https://doi.org/10.1007/s00018-009-0147-7

    • PubMed
    • Google Scholar
70. 1. Wohlfert EA
    2. Warunek J
    3. Jin RM
    4. Marzullo B

    (2020) Tbet - expressing Tregs protect against lethal immunopathology during T. gondii infection

    Journal of Immunology 5:931–943.

    https://doi.org/10.4049/immunohorizons.2100080

    • PubMed
    • Google Scholar
71. 1. Xie L
    2. Pi X
    3. Townley-Tilson WHD
    4. Li N
    5. Wehrens XHT
    6. Entman ML
    7. Taffet GE
    8. Mishra A
    9. Peng J
    10. Schisler JC
    11. Meissner G
    12. Patterson C

    (2015) PHD2/3-dependent hydroxylation tunes cardiac response to β-adrenergic stress via phospholamban

    The Journal of Clinical Investigation 125:2759–2771.

    https://doi.org/10.1172/JCI80369

    • PubMed
    • Google Scholar
72. 1. Xing Y
    2. Hogquist KA

    (2012) T-cell tolerance: central and peripheral

    Cold Spring Harbor Perspectives in Biology 4:1–15.

    https://doi.org/10.1101/cshperspect.a006957

    • PubMed
    • Google Scholar
73. 1. Yamamoto A
    2. Hester J
    3. Macklin PS
    4. Kawai K
    5. Uchiyama M
    6. Biggs D
    7. Bishop T
    8. Bull K
    9. Cheng X
    10. Cawthorne E
    11. Coleman ML
    12. Crockford TL
    13. Davies B
    14. Dow LE
    15. Goldin R
    16. Kranc K
    17. Kudo H
    18. Lawson H
    19. McAuliffe J
    20. Milward K
    21. Scudamore CL
    22. Soilleux E
    23. Issa F
    24. Ratcliffe PJ
    25. Pugh CW

    (2019) Systemic silencing of PHD2 causes reversible immune regulatory dysfunction

    The Journal of Clinical Investigation 129:3640–3656.

    https://doi.org/10.1172/JCI124099

    • PubMed
    • Google Scholar

Author details

1. Yousra Ajouaou

   1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
   2. Immunobiology Laboratory, Université Libre de Bruxelles (ULB), Charleroi, Belgium

   Contribution

   Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Validation, Visualization, Writing - original draft, Writing - review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0002-1734-6505

2. Abdulkader Azouz

   1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
   2. Institute for Medical Immunology, Université Libre de Bruxelles (ULB), Charleroi, Belgium

   Contribution

   Data curation, Formal analysis, Software, Visualization, Writing - review and editing

   Competing interests

   No competing interests declared

3. Anaëlle Taquin

   1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
   2. Immunobiology Laboratory, Université Libre de Bruxelles (ULB), Charleroi, Belgium

   Contribution

   Investigation, Methodology, She performed additional experiments and contributed to data analysis, She performed additional experiments and contributed to data analysis

   Competing interests

   No competing interests declared

4. Sebastien Denanglaire

   1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
   2. Immunobiology Laboratory, Université Libre de Bruxelles (ULB), Charleroi, Belgium

   Contribution

   Methodology

   Competing interests

   No competing interests declared

5. Hind Hussein

   1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
   2. Immunobiology Laboratory, Université Libre de Bruxelles (ULB), Charleroi, Belgium

   Contribution

   Methodology, She performed additional experiments and contributed to data analysis, She performed additional experiments and contributed to data analysis

   Competing interests

   No competing interests declared

6. Mohammad Krayem

   1. Department of Radiation Oncology, Institut Jules Bordet, Université Libre de Bruxelles, Brussels, Belgium
   2. Laboratory of Clinical and Experimental Oncology (LOCE), Institut Jules Bordet, Université Libre de Bruxelles, Brussels, Belgium

   Contribution

   Methodology

   Competing interests

   No competing interests declared

7. Fabienne Andris

   1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
   2. Immunobiology Laboratory, Université Libre de Bruxelles (ULB), Charleroi, Belgium

   Contribution

   Supervision, Writing - review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0002-8644-1020

8. Muriel Moser

   1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
   2. Immunobiology Laboratory, Université Libre de Bruxelles (ULB), Charleroi, Belgium

   Contribution

   Funding acquisition, Project administration, Resources, Supervision, Writing - review and editing

   Competing interests

   No competing interests declared

9. Stanislas Goriely

   1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
   2. Immunobiology Laboratory, Université Libre de Bruxelles (ULB), Charleroi, Belgium
   3. Institute for Medical Immunology, Université Libre de Bruxelles (ULB), Charleroi, Belgium

   Contribution

   Project administration, Resources, Writing - review and editing

   Competing interests

   No competing interests declared

10. Oberdan Leo

    1. U-CRI (ULB Center for Research in Immunology), Université Libre de Bruxelles (ULB), Charleroi, Belgium
    2. Immunobiology Laboratory, Université Libre de Bruxelles (ULB), Charleroi, Belgium

    Contribution

    Conceptualization, Funding acquisition, Methodology, Project administration, Resources, Supervision, Validation, Writing - original draft, Writing - review and editing

    For correspondence

    oberdan.leo@ulb.be

    Competing interests

    No competing interests declared

    "This ORCID iD identifies the author of this article:" 0000-0002-3621-4743

• 1,401

  views

• 197

  downloads

• 4

  citations

Views, downloads and citations are aggregated across all versions of this paper published by eLife.