Increased levels of regulatory T cells (Tregs) in human immunodeficiency virus‐infected patients after 5 years of highly active anti‐retroviral therapy may be due to increased thymic production of naive Tregs

This study determines levels of regulatory T cells (T_regs), naive T_regs, immune activation and cytokine patterns in 15 adult human immunodeficiency virus (HIV)‐infected patients receiving prolonged highly active anti‐retroviral therapy (HAART) who have known thymic output, and explores if naive T_regs may represent recent thymic emigrant T_regs. HIV‐infected patients treated with HAART with a median of 1 and 5 years were compared with healthy controls. Percentages of T_regs (CD3⁺CD4⁺CD25⁺CD127^low), naive T_regs (CD3⁺CD4⁺CD25⁺CD45RA⁺) and activation markers (CD38⁺human leucocyte antigen D‐related) were determined by flow cytometry. Forkhead box P3 mRNA expression and T cell receptor excision circles (T_REC) content in CD4⁺ cells were determined by polymerase chain reaction and cytokines analysed with Luminex technology. Levels of T_regs were significantly higher in HIV‐infected patients compared with controls, both after 1 and 5 years of HAART (P < 0·001), despite fully suppressed HIV‐RNA and normalization of both CD4 counts, immune activation and cytokine patterns. Furthermore, levels of naive T_regs were elevated significantly in HIV‐infected patients (P < 0·001) and were associated with thymic output measured as the T_REC frequency in CD4⁺ cells (P = 0·038). In summary, T_reg levels in HIV‐infected patients are elevated even after 5 years of HAART. Increased thymic production of naive T_regs may contribute to higher T_reg levels in HIV‐infection.     

Association between discordant immunological response to highly active anti‐retroviral therapy,regulatory T cell percentage,immune cell activation and very low‐level viraemia in HIV‐infected patients

The mechanisms sustaining the absence of complete immune recovery in HIV‐infected patients upon long‐term effective highly active anti‐retroviral therapy (HAART) remain elusive. Immune activation, regulatory T cells (T_regs) or very low‐level viraemia (VLLV) have been alternatively suspected, but rarely investigated simultaneously. We performed a cross‐sectional study in HIV‐infected aviraemic subjects (mean duration of HAART: 12 years) to concomitantly assess parameters associated independently with inadequate immunological response. Patients were classified as complete immunological responders (cIR, n = 48) and inadequate immunological responders (iIR, n = 39), depending on the CD4⁺ T cell count (> or < 500/mm³). Clinical and virological data (including very low‐level viraemia) were collected. In parallel, immunophenotyping of CD4⁺ lymphocytes, including T_reg subsets, and CD8⁺ T cells was performed. Percentages of activated CD4⁺ T cells, T_regs, effector T_regs and terminal effector T_regs were found to be significantly elevated in iIR. Neither the percentage of activated CD8⁺ T cells nor VLLV were found to be associated with iIR. In the multivariate analysis, nadir of CD4⁺ T cell count and percentage of T_regs were the only two parameters associated independently with iIR [odds ratio (OR) = 2·339, P = 0·001, and OR = 0·803, P = 0·041]. We present here the largest study investigating simultaneously the immune response to long‐term HAART, activation of CD4⁺ and CD8⁺ T cells, T_reg percentages and very low‐level viraemia. Causative interactions between T_regs and CD4⁺ T cells should now be explored prospectively in a large patients cohort.     

Two separate effects contribute to regulatory T cell defect in systemic lupus erythematosus patients and their unaffected relatives

Forkhead box P3 (FoxP3)⁺ regulatory T cells (T_regs) are functionally deficient in systemic lupus erythematosus (SLE), characterized by reduced surface CD25 [the interleukin (IL)‐2 receptor alpha chain]. Low‐dose IL‐2 therapy is a promising current approach to correct this defect. To elucidate the origins of the SLE T_reg phenotype, we studied its role through developmentally defined regulatory T cell (T_reg) subsets in 45 SLE patients, 103 SLE‐unaffected first‐degree relatives and 61 unrelated healthy control subjects, and genetic association with the CD25‐encoding IL2RA locus. We identified two separate, uncorrelated effects contributing to T_reg CD25. (1) SLE patients and unaffected relatives remarkably shared CD25 reduction versus controls, particularly in the developmentally earliest CD4⁺FoxP3⁺CD45RO^–CD31⁺ recent thymic emigrant T_regs. This first component effect influenced the proportions of circulating CD4⁺FoxP3^highCD45RO⁺ activated T_regs. (2) In contrast, patients and unaffected relatives differed sharply in their activated T_reg CD25 state: while relatives as control subjects up‐regulated CD25 strongly in these cells during differentiation from naive T_regs, SLE patients specifically failed to do so. This CD25 up‐regulation depended upon IL2RA genetic variation and was related functionally to the proliferation of activated T_regs, but not to their circulating numbers. Both effects were found related to T cell IL‐2 production. Our results point to (1) a heritable, intrathymic mechanism responsible for reduced CD25 on early T_regs and decreased activation capacity in an extended risk population, which can be compensated by (2) functionally independent CD25 up‐regulation upon peripheral T_reg activation that is selectively deficient in patients. We expect that T_reg‐directed therapies can be monitored more effectively when taking this distinction into account.     

Depletion of CD4+CD25+ regulatory T cells enhances natural killer T cell‐mediated anti‐tumour immunity in a murine mammary breast cancer model

Both invariant natural killer T (NK T) cells and CD4⁺CD25⁺ T regulatory cells (T_regs) regulate the immune system to maintain homeostasis. In a tumour setting, NK T cells activated by α‐galactosylceramide (α‐GalCer) execute anti‐tumour activity by secreting cytokines. By contrast, T_regs intrinsically suppress antigen‐specific immune responses and are often found to be elevated in tumour patients. In this study, we have shown that T_regs regulate NK T cell function negatively in vitro, suggesting a direct interaction between these cell types. In a murine mammary tumour model, we demonstrated that administration of either α‐GalCer or anti‐CD25 antibody alone markedly suppressed tumour formation and pulmonary metastasis, and resulted in an increase in the survival rate up to 44% (from a baseline of 0%). When treatments were combined, depletion of T_regs boosted the anti‐tumour effect of α‐GalCer, and the survival rate jumped to 85%. Our results imply a potential application of combining T_reg cell depletion with α‐GalCer to stimulate NK T cells for cancer therapy.     

The role of regulatory T cell (Treg) subsets in gestational diabetes mellitus

Physiological changes during normal pregnancy are characterized by an inflammatory immune response and insulin resistance. Therefore, we hypothesize that gestational diabetes mellitus (GDM) may be caused by an inappropriate adaption of the maternal immune system to pregnancy. In this study we examined the role of regulatory T cell (T_reg) differentiation for the development of GDM during pregnancy. We used six-colour flow cytometric analysis to demonstrate that the total CD4⁺CD127^low+/−CD25⁺ forkhead box protein 3 (FoxP3⁺) T_reg pool consists of four different T_reg subsets: naive CD45RA⁺ T_regs, HLA-DR⁻CD45RA⁻ memory T_regs (DR⁻ T_regs) and the highly differentiated and activated HLA-DR^low+CD45RA⁻ and HLA-DR^high+CD45RA⁻ memory T_regs (DR^low+ and DR^high+ T_regs). Compared to healthy pregnancies, the percentage of CD4⁺CD127^low+/−CD25⁺FoxP3⁺ T_regs within the total CD4⁺ T helper cell pool was not different in patients affected by GDM. However, the suppressive activity of the total CD4⁺CD127^low+/−CD25⁺ T_reg pool was significantly reduced in GDM patients. The composition of the total T_reg pool changed in the way that its percentage of naive CD45RA⁺ T_regs was decreased significantly in both patients with dietary-adjusted GDM and patients with insulin-dependent GDM. In contrast, the percentage of DR⁻-memory T_regs was increased significantly in patients with dietary-adjusted GDM, while the percentage of DR^low+ and DR^high+ memory T_regs was increased significantly in patients with insulin-dependent GDM. Hence, our findings propose that alterations in homeostatic parameters related to the development and function of naive and memory T_regs may cause the reduction of the suppressive capacity of the total T_reg pool in GDM patients. However, as this is an exploratory analysis, the results are only suggestive and require further validation.     

Significant augmentation of regulatory T cell numbers occurs during the early neonatal period

Regulatory T cells (T_regs) control immune responses by suppressing various inflammatory cells. T_regs in newborn babies may play an important role in preventing excessive immune responses during their environmental change. We examined the number and phenotype of T_regs during the neonatal period in 49 newborn babies. T_regs were characterized by flow cytometry using cord blood (CB) and peripheral blood (PB) from the early (7–8 days after birth) and late (2–4 weeks after birth) neonatal periods. CD4⁺forkhead box protein 3 (FoxP3⁺) T cells were classified into resting T_regs (CD45RA⁺FoxP3^low), activated T_regs (CD45RA^– FoxP3^high) and newly activated T cells (CD45RA^– FoxP3^low). Compared with CB and PB during the late neonatal period, the percentage of T_regs and all T_reg subpopulations in the CD4⁺ lymphocyte population were increased significantly during the early neonatal period. Furthermore, the proportion and absolute number of activated T_regs were increased markedly compared with other T_reg subpopulations, such as resting T_regs and newly activated T cells (non‐T_regs), in the early neonatal period. Increased T_regs concomitantly expressed the suppressive molecule cytotoxic T lymphocyte antigen‐4 (CTLA‐4). The up‐regulated expression of chemokine receptor 4 (CCR4) and down‐regulated expression of CCR7 were also observed in expanded T_regs. When cord blood cells were cultured in vitro with CD3 monoclonal antibodies (mAb) for 5 days, CD4⁺CD45RA^–FoxP3^high cells were increased significantly during the culture. Thus, the presence of increased activated T_regs in early neonates may play an important role in immunological regulation by suppressing excessive T cell activation caused by the immediate exposure to ubiquitous antigens after birth.     

Regulatory T cell frequencies are increased in preterm infants with clinical early‐onset sepsis

The predisposition of preterm neonates to invasive infection is, as yet, incompletely understood. Regulatory T cells (T_regs) are potential candidates for the ontogenetic control of immune activation and tissue damage in preterm infants. It was the aim of our study to characterize lymphocyte subsets and in particular CD4⁺CD25⁺forkhead box protein 3 (FoxP3)⁺ T_regs in peripheral blood of well‐phenotyped preterm infants (n = 117; 23 + 0 – 36 + 6 weeks of gestational age) in the first 3 days of life in comparison to term infants and adults. We demonstrated a negative correlation of T_reg frequencies and gestational age. T_regs were increased in blood samples of preterm infants compared to term infants and adults. Notably, we found an increased T_reg frequency in preterm infants with clinical early‐onset sepsis while cause of preterm delivery, e.g. chorioamnionitis, did not affect T_reg frequencies. Our data suggest that T_regs apparently play an important role in maintaining maternal‐fetal tolerance, which turns into an increased sepsis risk after preterm delivery. Functional analyses are needed in order to elucidate whether T_regs have potential as future target for diagnostics and therapeutics.     

Transforming growth factor beta 1 plays an important role in inducing CD4+CD25+forhead box P3+ regulatory T cells by mast cells

The role of mast cells (MCs) in the generation of adaptive immune responses especially in the transplant immune responses is far from being resolved. It is reported that mast cells are essential intermediaries in regulatory T cell (T_reg) transplant tolerance, but the mechanism has not been clarified. To investigate whether bone marrow‐derived mast cells (BMMCs) can induce T_regs by expressing transforming growth factor beta 1 (TGF‐β1) in vitro, bone marrow cells obtained from C57BL/6 (H‐2^b) mice were cultured with interleukin (IL)‐3 (10 ng/ml) and stem cell factor (SCF) (10 ng/ml) for 4 weeks. The purity of BMMCs was measured by flow cytometry. The BMMCs were then co‐cultured with C57BL/6 T cells at ratios of 1:2, 1:1 and 2:1. Anti‐CD3, anti‐CD28 and IL‐2 were administered into the co‐culture system with (experiment groups) or without (control groups) TGF‐β1 neutralizing antibody. The percentages of CD4⁺CD25⁺forkhead box P3 (FoxP3)⁺ T_regs in the co‐cultured system were analysed by flow cytometry on day 5. The T_reg percentages were significantly higher in all the experiment groups compared to the control groups. These changes were deduced by applying TGF‐β1 neutralizing antibody into the co‐culture system. Our results indicated that the CD4⁺ T cells can be induced into CD4⁺CD25⁺FoxP3⁺ T cells by BMMCs via TGF‐β1.     

Control of immune responses by immunoregulatory T cells

Immunoregulatory T cells play a key role in modifying the immune responses to self antigens, tumor antigens, and pathogenic organisms. This review summarizes recent data on naturally occurring CD4⁺ regulatory T cells that constitutively express CD25 (CD25⁺T_reg). We examine the markers that can be used to differentiate these cells from effector T cells, what is known about their mode of action in controlling the activity of effector T cells, the antigenic specificity of CD25⁺T_reg, and their ability to survive and to be selected in vivo. We also summarize specific information on the role of CD25⁺T_reg in controlling anti-tumor responses, an area were manipulation of this subset holds particular clinical promise.     

In‐vitro effect of pembrolizumab on different T regulatory cell subsets

Programmed death‐1 (PD‐1) and interactions with PD‐ligand 1 (PD‐L1) play critical roles in the tumour evasion of immune responses through different mechanisms, including inhibition of effector T cell proliferation, reducing cytotoxic activity, induction of apoptosis in tumour‐infiltrating T cells and regulatory T cell (T_reg) expansion. Effective blockade of immune checkpoints can therefore potentially eliminate these detrimental effects. The aim of this study was to investigate the effect of anti‐PD‐1 antibody, pembrolizumab, on various T_reg subpopulations. Peripheral blood mononuclear cells (PBMC) from healthy donors (HD) and primary breast cancer patients (PBC) were treated in vitro with pembrolizumab, which effectively reduced PD‐1 expression in both cohorts. We found that PD‐1 was expressed mainly on CD4⁺CD25⁺ T cells and pembrolizumab had a greater effect on PD‐1 expression in CD4⁺CD25^? T cells, compared to CD4⁺CD25⁺ cells. In addition, pembrolizumab did not affect the expression levels of T_reg‐related markers, including cytotoxic T lymphocyte antigen‐4 (CTLA‐4), CD15s, latency‐associated peptide (LAP) and Ki‐67. Moreover, we report that CD15s is expressed mainly on forkhead box P3 (FoxP3)^?Helios⁺ T_reg in HD, but it is expressed on FoxP3⁺Helios^? T_reg subset in addition to FoxP3^?Helios⁺ T_reg in PBC. Pembrolizumab did not affect the levels of FoxP3^+/?Helios^+/? T_reg subsets in both cohorts. Taken together, our study suggests that pembrolizumab does not affect T_reg or change their phenotype or function but rather blocks signalling via the PD‐1/PD‐L1 axis in activated T cells.     

Obtaining regulatory T cells from uraemic patients awaiting kidney transplantation for use in clinical trials

Adoptive transfer of regulatory T cells (T_regs) has been proposed for use as a cellular therapy to induce transplantation tolerance. Preclinical data are encouraging, and clinical trials with T_reg therapy are anticipated. In this study, we investigate different strategies for the isolation and expansion of CD4⁺CD25^highCD127^low T_regs from uraemic patients. We use allogeneic dendritic cells (DCs) as feeder cells for the expansion and compare T_reg preparations isolated by either fluorescence activated cell sorting (FACS) or magnetic activated cell sorting (MACS) that have been expanded subsequently with either mature or tolerogenic DCs. Expanded T_reg preparations have been characterized by their purity, cytokine production and in‐vitro suppressive ability. The results show that T_reg preparations can be isolated from uraemic patients by both FACS and MACS. Also, the type of feeder cells used in the expansion affects both the purity and the functional properties of the T_reg preparations. In particular, FACS‐sorted T_reg preparations expanded with mature DCs secrete more interleukin (IL)‐10 and granzyme B than FACS‐sorted T_reg preparations expanded with tolerogenic DCs. This is a direct comparison between different isolation techniques and expansion protocols with T_regs from uraemic patients that may guide future efforts to produce clinical‐grade T_regs for use in kidney transplantation.     

Altered regulatory T cell phenotype in latent autoimmune diabetes of the adults (LADA)

Latent autoimmune diabetes of the adults (LADA) accounts for up to 12% of all patients with diabetes. Initially the disease resembles type 2 diabetes (T2D); however, the typical presence of β cell autoantibodies indicates an autoimmune basis of LADA. While dysfunctional regulatory T cells (T_regs) have been implicated in autoimmune diabetes, these cells have been scarcely studied in LADA. The aim of this study was to investigate the frequency and phenotype of circulating T_regs in LADA patients early during disease progression. Flow cytometric analysis was performed on whole blood and peripheral mononuclear cells (PBMC) from patients diagnosed with LADA prior to insulin deficiency (n = 39) and from healthy volunteers (n = 20). Overall, we found the frequency and activation status of peripheral putative T_regs to be altered in LADA patients compared to healthy controls. While total T cells and CD4⁺ T cells expressing high levels of CD25 (CD4⁺CD25^hi) were unchanged, the frequency and total numbers of CD4⁺ T cells expressing an intermediate level of CD25 (CD4⁺CD25^int) were decreased in LADA patients. Interestingly, the expression of the T_reg‐specific marker forkhead box protein 3 (FoxP3), as well as the activation and memory makers CD69, cytotoxic T lymphocyte associated antigen 4 (CTLA‐4), CCR4 and CD45RO were increased in CD4⁺CD25⁺ T cells of the patients. Our data depict phenotypical changes in T cells of LADA patients that may reflect a derangement in peripheral immune regulation contributing to the slow process leading to insulin‐dependent diabetes in these patients.     

Regulatory T cells and chronic immune activation in human immunodeficiency virus 1 (HIV-1)-infected children

The function of CD4⁺ T cells with regulatory activity (T_regs) is the down-regulation of immune responses. This suppressive activity may limit the magnitude of effector responses, resulting in failure to control human immunodeficiency virus 1 (HIV-1) infection, but may also suppress chronic immune activation, a characteristic feature of HIV-1 disease. We evaluated the correlation between viral load, immune activation and T_regs in HIV-1-infected children. Eighty-nine HIV-1-infected children (aged 6–14 years) were included in the study and analysed for HIV-1 plasmaviraemia, HIV-1 DNA load, CD4 and CD8 cell subsets. T_reg cells [CD4⁺ CD25^highCD127^lowforkhead box P3 (FoxP3^high)] and CD8-activated T cells (CD8⁺CD38⁺) were determined by flow cytometry. Results showed that the number of activated CD8⁺CD38⁺ T cells increased in relation to HIV-1 RNA plasmaviraemia (r = 0·403, P < 0·0001). The proportion of T_regs also correlated positively with HIV-1 plasmaviraemia (r = 0·323, P = 0·002), but correlated inversely with CD4⁺ cells (r = −0·312, P = 0·004), thus suggesting a selective expansion along with increased viraemia and CD4⁺ depletion. Interestingly, a positive correlation was found between the levels of T_regs and CD8⁺CD38⁺ T cells (r = 0·305, P = 0·005), and the percentage of T_regs tended to correlate with HIV-1 DNA load (r = 0·224, P = 0·062). Overall, these findings suggest that immune activation contributes to the expansion of T_reg cells. In turn, the suppressive activity of T_regs may impair effector responses against HIV-1, but appears to be ineffective in limiting immune activation.     

Chemotherapy alters the increased numbers of myeloid-derived suppressor and regulatory T cells in children with acute lymphoblastic leukemia

Introduction: Acute lymphoblastic leukemia (ALL) is the most common cancer diagnosed in children. The precise mechanism behind the relapse in this disease is not clearly known. One possible mechanism could be the accumulation of immunosuppressive cells, including myeloid-derived suppressor cells (MDSCs) and T regulatory cells (T_regs) which we and others have reported to mediate suppression of anti-tumor immune responses.

Aim: In this study, we aimed to analyze the numbers of these cells in a population of B-ALL pediatric patients.

Methods: Peripheral blood samples withdrawn from B-ALL pediatric patients (n?=?45 before, during and after the induction phase of chemotherapy. Using multi parametric flow cytometric analysis. MDSCs were identified as Lin^–HLA-DR^–CD33⁺CD11b⁺; and T_reg cells were defined as CD4⁺CD25⁺CD127^–/low.

Results: Early diagnosed B-ALL patients showed significant increases in the numbers of MDSCs and T_regs as compared to healthy volunteers. During induction of chemotherapy, however, the patients showed higher and lower numbers of MDSCs and T_reg cells, respectively as compared to early diagnosed patients (i.e., before chemotherapy). After induction of chemotherapy, the numbers of MDSCs and T_reg cells showed higher increases and decreases, respectively as compared to the numbers in patients during chemotherapy.

Conclusion: Our results indicate that B-ALL patients harbor high numbers of both MDSCs and T_regs cells. This pilot study opens a new avenue to investigate the mechanism mediating the emergence of these cells on larger number of B-ALL patients at different treatment stages.     

An increased CD25‐positive intestinal regulatory T lymphocyte population is dependent upon Cox‐2 activity in the Apcmin/+ model

Only mismatch repair (MMR)‐deficient colorectal cancer (CRC) appears to respond well to programmed death (PD)‐1 inhibition at the present time. Emerging evidence suggests a role for micro‐environmental factors such as CD25⁺ cells modulating response to PD‐1 inhibition. In the Apc^Min/+ model of familial adenomatous polyposis (MMR‐proficient CRC), increased Cyclooxygenase‐2 (Cox‐2) expression by cells which include alternatively activated mononuclear phagocytes promotes intestinal tumorigenesis by mechanisms which may include immune suppression. To gain insight into this, we compared regulatory T cell (T_reg) populations between Apc^Min/+ and wild‐type mice prior to and after the phase of increased intestinal Cox‐2‐dependent prostaglandin E₂ (PGE₂) production. There was no difference in systemic T_reg function or numbers between Apc^Min/+ and wild‐type mice. However, increased numbers of small intestinal CD25⁺ T_regs were observed with increased Cox‐2 activity in the absence of any difference in the expression of Tgf‐β or Tslp between Apc^Min/+ and wild‐type mice. Cox‐2 inhibitor therapy (Celecoxib) reversed the increase in Apc^Min/+ intestinal CD25⁺ T_reg numbers, without decreasing numbers of CD25⁺ systemic T_regs. Forkhead box protein 3 (FoxP3⁺) and Cox‐2⁺ cells were co‐localized to the interstitium of adenomas of Apc^min/+ mice. These results suggest selective dependence of an ‘activated T_reg’ phenotype on paracrine Cox‐2 activity in Apc^Min/+ small intestine. For therapeutic potential, further studies are required to evaluate the relevance of these findings to human cancer as well as the functional significance of CD25⁺ intestinal T_regs in cancer.     

Helicobacter pylori induces in-vivo expansion of human regulatory T cells through stimulating interleukin-1β production by dendritic cells

Helicobacter pylori is one of the most common infections in the world. Despite inciting inflammation, immunological clearance of the pathogen is often incomplete. CD4⁺CD25^hiforkhead box protein 3 (FoxP3⁺) regulatory T cells (T_regs) are potent suppressors of different types of immune responses and have been implicated in limiting inflammatory responses to H. pylori. Investigating the influence of H. pylori on T_reg function and proliferation, we found that H. pylori-stimulated dendritic cells (DCs) induced proliferation in T_regs and impaired their suppressive capability. This effect was mediated by interleukin (IL)-1β produced by H. pylori-stimulated DCs. These data correlated with in-vivo observations in which H. pylori⁺ gastric mucosa contained more T_regs in active cell division than uninfected stomachs. Inciting local proliferation of T_regs and inhibiting their suppressive function may represent a mechanism for the chronic gastritis and carcinogenesis attributable to H. pylori.     

CD4+HLA-G+ regulatory T cells: Molecular signature and pathophysiological relevance

The regulation of potentially harmful immune responses by regulatory T (T_reg) cells is essential for maintaining peripheral immune tolerance and homeostasis. Especially CD4⁺ T_reg cells have been regarded as pivotal regulators of autoreactive and inflammatory responses as well as inducers of immune tolerance by using a variety of immune suppressive mechanisms.Besides the well-known classical CD4⁺CD25⁺FoxP3⁺ T_reg cells, CD4⁺ T cells expressing the immune tolerizing molecule human leukocyte antigen G (HLA-G) have been recently described as another potent thymus-derived T_reg (tT_reg) cell subset. Albeit both tT_reg subsets share common molecular characteristics, the mechanisms of their immunosuppressive function differ fundamentally. Dysfunction and numerical abnormalities of classical CD4⁺ tT_reg cells have been implicated in the pathogenesis of several immune-mediated diseases such as multiple sclerosis (MS). Clearly, a deeper understanding of the various CD4⁺ tT_reg subsets and also the underlying mechanisms of impaired immune tolerance in these disorders are essential for the development of potential therapeutic strategies.This review focuses on the current knowledge on defining features and functioning of HLA-G⁺CD4⁺ tT_reg cells as well as their emerging role in various pathologies with special emphasis on the pathogenesis of MS. Furthermore, future research possibilities together with potential therapeutic applications are discussed.     

Immunological monitoring of extracorporeal photopheresis after heart transplantation

Extracorporeal photopheresis (ECP) has been used as a prophylactic and therapeutic option to avoid and treat rejection after heart transplantation (HTx). Tolerance‐inducing effects of ECP such as up‐regulation of regulatory T cells (T_regs) are known, but specific effects of ECP on regulatory T cell (T_reg) subsets and dendritic cells (DCs) are lacking. We analysed different subsets of T_regs and DCs as well as the immune balance status during ECP treatment after HTx. Blood samples were collected from HTx patients treated with ECP for prophylaxis (n = 9) or from patients with histologically proven acute cellular rejection (ACR) of grade ≥ 1B (n = 9), as well as from control HTx patients without ECP (HTxC; n = 7). Subsets of T_regs and DCs as well as different cytokine levels were analysed. Almost 80% of the HTx patients showed an effect to ECP treatment with an increase of T_regs and plasmacytoid DCs (pDCs). The percentage of pDCs before ECP treatment was significantly higher in patients with no ECP effect (26·3% ± 5·6%) compared to patients who showed an effect to ECP (9·8% ± 10·2%; P = 0·011). Analysis of functional subsets of CD4⁺CD25^highCD127^low T_regs showed that CD62L‐, CD120b‐ and CD147‐positive T_regs did not differ between the groups. CD39‐positive T_regs increased during ECP treatment compared to HTxC. ECP‐treated patients showed higher levels for T helper type 1 (Th1), Th2 and Th17 cytokines. Cytokine levels were higher in HTx patients with rejection before ECP treatment compared to patients with prophylactic ECP treatment. We recommend a monitoring strategy that includes the quantification and analysis of T_regs, pDCs and the immune balance status before and up to 12 months after starting ECP.     

Emerging patterns of regulatory T cell function in tuberculosis

Tuberculosis (TB) is one of the top 10 causes of mortality worldwide from a single infectious agent and has significant implications for global health. A major hurdle in the development of effective TB vaccines and therapies is the absence of defined immune-correlates of protection. In this context, the role of regulatory T cells (T_reg), which are essential for maintaining immune homeostasis, is even less understood. This review aims to address this knowledge gap by providing an overview of the emerging patterns of T_reg function in TB. Increasing evidence from studies, both in animal models of infection and TB patients, points to the fact the role of T_regs in TB is dependent on disease stage. While T_regs might expand and delay the appearance of protective responses in the early stages of infection, their role in the chronic phase perhaps is to counter-regulate excessive inflammation. New data highlight that this important homeostatic role of T_regs in the chronic phase of TB may be compromised by the expansion of activated human leucocyte antigen D-related (HLA-DR)⁺CD4⁺ suppression-resistant effector T cells. This review provides a comprehensive and critical analysis of the key features of T_reg cells in TB; highlights the importance of a balanced immune response as being important in TB and discusses the importance of probing not just T_reg frequency but also qualitative aspects of T_reg function as part of a comprehensive search for novel TB treatments.     

Critical roles of regulatory B and T cells in helminth parasite-induced protection against allergic airway inflammation

The prevalence of allergic asthma and incidences of helminth infections in humans are inversely correlated. Although experimental studies have established the causal relation between parasite infection and allergic asthma, the mechanism of the parasite-associated immunomodulation is not fully elucidated. Using a murine model of asthma and nematode parasite Heligmosomoides polygyrus, we investigated the roles of regulatory B cells (B_reg) and T cells (T_reg) in mediation of the protection against allergic asthma by parasite. H. polygyrus infection significantly suppressed ovalbumin (OVA)-induced allergic airway inflammation (AAI) evidenced by alleviated lung histopathology and reduced numbers of bronchoalveolar inflammatory cell infiltration, and induced significant responses of interleukin (IL)-10⁺ B_reg, IL-10⁺ T_reg and forkhead box protein 3 (FoxP3)⁺ T_reg in mesenteric lymph node and spleen of the mice. Adoptive transfer of IL-10⁺ B_reg and IL-10⁺ T_reg cell prevented the lung immunopathology in AAI mice. Depletion of FoxP3⁺ T_reg cells in FoxP3-diphtheria toxin (DT) receptor transgenic mice by diphtheria toxin (DT) treatment exacerbated airway inflammation in parasite-free AAI mice and partially abrogated the parasite-induced protection against AAI. IL-10⁺ B_reg cells were able to promote IL-10⁺ T_reg expansion and maintain FoxP3⁺ T_reg cell population. These two types of T_regs failed to induce CD19⁺ B cells to transform into IL-10⁺ B_reg cells. These results demonstrate that B_reg, IL-10⁺ T_reg and FoxP3⁺ T_reg cells contribute in A discrepant manner to the protection against allergic airway immunopathology by parasiteS. B_reg cell might be a key upstream regulatory cell that induces IL-10⁺ T_reg response and supports FoxP3⁺ T_reg cell population which, in turn, mediate the parasite-imposed immunosuppression of allergic airway inflammation. These results provide insight into the immunological relationship between parasite infection and allergic asthma.