Differential control of Helios(+/-) Treg development by monocyte subsets through disparate inflammatory cytokines

Exosomes, MDSCs and Tregs: A new frontier for GVHD prevention and treatment

The development of graft versus host disease (GVHD) represents a long-standing complication of allogeneic hematopoietic cell transplantation (allo-HCT). Different approaches have been used to control the development of GVHD with most relying on variations of chemotherapy drugs to eliminate allo-reactive T cells. While these approaches have proven effective, it is generally accepted that safer, and less toxic GVHD prophylaxis drugs are required to reduce the health burden placed on allo-HCT recipients. In this review, we will summarize the emerging concepts revolving around three biologic-based therapies for GVHD using T regulatory cells (Tregs), myeloid-derived-suppressor-cells (MDSCs) and mesenchymal stromal cell (MSC) exosomes. This review will highlight how each specific modality is unique in its mechanism of action, but also share a common theme in their ability to preferentially activate and expand Treg populations in vivo. As these three GVHD prevention/treatment modalities continue their path toward clinical application, it is imperative the field understand both the biological advantages and disadvantages of each approach.

Coexpression of Helios in Foxp3+ Regulatory T Cells and Its Role in Human Disease

Regulatory T cells (Tregs) expressing the Foxp3 transcription factor are indispensable for the maintenance of immune system homeostasis. Tregs may lose Foxp3 expression or be reprogrammed into cells that produce proinflammatory cytokines, for example, Th1-like Tregs, Th2-like Tregs, Th17-like Tregs, and Tfh-like Tregs. Accordingly, selective therapeutic molecules that manipulate Treg lineage stability and/or functional activity might have the potential to improve aberrant immune responses in human disorders. In particular, the transcription factor Helios has emerged as an important marker and modulator of Tregs. Therefore, the current review focuses on recent findings on the expression, function, and mechanisms of Helios, as well as the patterns of Foxp3⁺ Tregs coexpressing Helios in various human disorders, in order to explore the potential of Helios for the improvement of many immune-related diseases. The studies were selected from PubMed using the library of the Nanjing Medical University in this review. The findings of the included studies indicate that Helios expression stabilizes the phenotype and function of Foxp3⁺ Tregs in certain inflammatory environments. Further, Tregs coexpressing Helios and Foxp3 were identified as a specific phenotype of stronger suppressor immune cells in both humans and animal models. Importantly, there is ample evidence that Helios-expressing Foxp3⁺ Tregs are relevant to various human disorders, including connective tissue diseases, infectious diseases, solid organ transplantation-related immunity, and cancer. Thus, Helios⁺Foxp3⁺CD4⁺ Tregs could be a valuable target in human diseases, and their potential should be explored further in the clinical setting.

Differences in Maturation Status and Immune Phenotypes of Circulating Helios+ and Helios- Tregs and Their Disrupted Correlations With Monocyte Subsets in Autoantibody-Positive T1D Individuals

CD4 Tregs are involved in the regulation of various autoimmune diseases but believed to be highly heterogeneous. Studies have indicated that Helios controls a distinct subset of functional Tregs. However, the immunological changes in circulating Helios⁺ and Helios⁻ Tregs are not fully explored in type 1 diabetes (T1D). Here, we elucidated the differences in maturation status and immune regulatory phenotypes of Helios⁺ and Helios⁻ Tregs and their correlations with monocyte subsets in T1D individuals. As CD25^−/low FOXP3⁺ Tregs also represent a subset of functional Tregs, we defined Tregs as FOXP3⁺CD127^−/low and examined circulating Helios⁺ and Helios⁻ Treg subpopulations in 68 autoantibody-positive T1D individuals and 68 age-matched healthy controls. We found that expression of both FOXP3 and CTLA4 diminished in Helios⁻ Tregs, while the proportion of CD25^−/low Tregs increased in Helios⁺ Tregs of T1D individuals. Although the frequencies of neither Helios⁺ nor Helios⁻ Tregs were affected by investigated T1D genetic risk loci, Helios⁺ Tregs correlated with age at T1D diagnosis negatively and disease duration positively. Moreover, the negative correlation between central and effector memory proportions of Helios⁺ Tregs in healthy controls was disrupted in T1D individuals. Finally, regulatory non-classical and intermediate monocytes also decreased in T1D individuals, and positive correlations between these regulatory monocytes and Helios⁺/Helios⁻ Treg subsets in healthy controls disappeared in T1D individuals. In conclusion, we demonstrated the alternations in maturation status and immune phenotypes in Helios⁺ and Helios⁻ Treg subsets and revealed the missing association between these Treg subsets and monocyte subsets in T1D individuals, which might point out another option for elucidating T1D mechanisms.

A Praziquantel Treatment Study of Immune and Transcriptome Profiles in Schistosoma haematobium-Infected Gabonese Schoolchildren

Background

Although Schistosoma haematobium infection has been reported to be associated with alterations in immune function, in particular immune hyporesponsiveness, there have been only few studies that have used the approach of removing infection by drug treatment to establish this and to understand the underlying molecular mechanisms.

Methods

Schistosoma haematobium-infected schoolchildren were studied before and after praziquantel treatment and compared with uninfected controls. Cellular responses were characterized by cytokine production and flow cytometry, and in a subset of children RNA sequencing (RNA-Seq) transcriptome profiling was performed.

Results

Removal of S haematobium infection resulted in increased schistosome-specific cytokine responses that were negatively associated with CD4+CD25+FOXP3+ T-cells and accompanied by increased frequency of effector memory T-cells. Innate responses to Toll like receptor (TLR) ligation decreased with treatment and showed positive association with CD4⁺CD25⁺FOXP3⁺ T-cells. At the transcriptome level, schistosome infection was associated with enrichment in cell adhesion, whereas parasite removal was associated with a more quiescent profile. Further analysis indicated that alteration in cellular energy metabolism was associated with S haematobium infection and that the early growth response genes 2 and 3 (EGR 2 and EGR3), transcription factors that negatively regulate T-cell activation, may play a role in adaptive immune hyporesponsiveness.

Conclusions

Using a longitudinal study design, we found contrasting effects of schistosome infection on innate and adaptive immune responses. Whereas the innate immune system appears more activated, the adaptive immunity is in a hyporesponsive state reflected in alterations in CD4⁺CD25⁺FOXP3⁺ T-cells, cellular metabolism, and transcription factors involved in anergy.

Foxp3+Helios+ regulatory T cells are associated with monocyte subsets and their PD-1 expression during acute HIV-1 infection

Background

Helios has been reported to stabilize regulatory T (Treg) suppressive function. Programmed cell death protein 1 (PD-1) expression in three human monocyte subsets modulates immune responses. Recently, our team reported that three monocyte subsets are associated with T helper cell differentiation in HIV-1-infected patients. Until now, the effects of monocyte subsets and their PD-1 expression on Foxp3⁺Helios⁺ Treg cells have not been fully characterized, especially during acute HIV-1 infection.

Results

The frequency of Foxp3⁺Helios⁺CD45RA⁺ Treg cells is significantly higher in patients with acute HIV-1 infection than those of healthy controls and chronic HIV-1-infected patients undergoing combined antiretroviral therapy. The frequency of Foxp3⁺Helios⁺CD45RA⁺ Treg cells is inversely correlated with CD4 T-cell counts and the CD4/CD8 ratio in chronic HIV-1-infected patients. During acute HIV-1 infection, the frequency of Foxp3⁺Helios⁺CD45RA⁺ Treg cells is inversely correlated with the frequency of the intermediate CD14⁺⁺CD16⁺ monocyte subset, but positively correlated with PD-1 expression in both intermediate CD14⁺⁺CD16⁺ and non-classical CD14⁺CD16⁺⁺ monocyte subsets.

Conclusions

In this study, the perturbations of Foxp3⁺Helios⁺ Treg cells were characterized, and the association between monocyte subsets and their PD-1 expression and Foxp3⁺Helios⁺ Treg cells was evaluated during HIV-1 infection. Our observations provide new evidence of the roles for Foxp3⁺Helios⁺ Treg cells and PD-1 expression on monocyte subsets in HIV pathogenesis.

Immunological Changes in Monocyte Subsets and Their Association With Foxp3+ Regulatory T Cells in HIV-1-Infected Individuals With Syphilis: A Brief Research Report

The incidence of syphilis has increased dramatically in men who have sex with men (MSM), especially those with HIV-1 infection. Treponema pallidum and HIV-1 are bidirectionally synergistic, accelerating disease progression reciprocally in co-infected individuals. We have shown that monocytes have different effects on T helper cells at different stages of HIV-1 infection. However, the immunological changes in the three monocyte subsets and in regulatory T cells (Tregs), and the associations between these cell types during syphilis infection among HIV-1-infected MSM remain unclear. Herein, we used cell staining methods to explore changes in monocyte subsets and Tregs and any associations between these cells. We found that the frequency of classical monocytes was higher in the rapid plasma reagin (RPR⁺) group than in the healthy controls (HCs) and the chronic HIV-1 infection (CHI) plus RPR⁺ (CHI&RPR⁺) group. The frequencies of Foxp3⁺CD25⁺CD45RA⁺ and Foxp3⁺Helios⁺CD45RA⁺ Tregs were significantly higher in the RPR⁺, CHI, and CHI&RPR⁺ groups than in HCs, whereas the frequency of CD45RA⁺ Tregs was lower in the CHI&RPR⁺ group than in CHI group. The frequencies of Foxp3⁺CD25⁺CD45RO⁺ and Foxp3⁺Helios⁺CD45RO⁺ Tregs were lower in the RPR⁺, CHI, and CHI&RPR⁺ groups than in HCs. The frequency of intermediate monocytes was inversely correlated with the frequency of CD45RA⁺ Tregs and positively correlated with the frequency of CD45RO⁺ Tregs. These results demonstrate for the first time that intermediate monocytes control the differentiation of Treg subsets in Treponema pallidum/HIV-1 co-infections. These findings provide new insights into an immunological mechanism involving monocytes/Tregs in HIV-infected individuals with syphilis.

Molecular mechanisms underlying Th1-like Treg generation and function

Since their ‘re-discovery’ more than two decades ago, FOXP3⁺ regulatory T cells (Tregs) have been an important subject of investigation in the biomedical field and our understanding of the mechanisms that drive their phenotype and function in health and disease has advanced tremendously. During the past few years it has become clear that Tregs are not a terminally differentiated population but show some degree of plasticity, and can, under specific environmental conditions, acquire the phenotype of effector T cells. In particular, recent works have highlighted the acquisition of a Th1-like phenotype by Tregs in several pathological environments. In this review we give an update on the concept of Treg plasticity and the advances in defining the molecular mechanisms that underlie the generation of Th1-like Tregs during an immune response and in different disease settings.

Immunoregulatory networks in sickle cell alloimmunization

Red blood cell (RBC) transfusions are critical for treatment and prevention of complications of sickle cell disease (SCD), and most SCD patients will receive 1 or more transfusions by age 20. However, SCD alloimmunization remains a serious complication of transfusions that can lead to life-threatening acute and delayed transfusion reactions. Alloimmunization rates are higher in SCD patients most likely due to RBC antigenic differences between largely white donors vs mainly African-American recipients and frequency of transfusions. However, it remains unclear why some but not all SCD patients develop alloantibodies. Cellular immune responses that differ between alloimmunized and nonalloimmunized SCD patients are beginning to be characterized. Altered CD4⁺ T helper cell responses, known to control immunoglobulin G production, have been identified in alloimmunized SCD patients, including abnormalities in regulatory T cells, as well as helper type 1 (T_H1), T_H17, and follicular helper T cells. Furthermore, heightened innate immune cell responses to cell free heme with cell polarization toward proinflammatory T cell profiles were recently reported in SCD antibody responders, suggesting that the ongoing hemolytic state in SCD may impair the ability of innate immune cells in these already alloimmunized patients to counter alloimmunization. Identification of molecular pathways in key cellular components that differ between alloimmunized and nonalloimmunized SCD patients is likely to lead to identification of biomarkers of alloimmunization and future design of targeted therapies to prevent or even dampen alloantibody responses in these highly susceptible patients.

Distinct Transcriptional and Anti-Mycobacterial Profiles of Peripheral Blood Monocytes Dependent on the Ratio of Monocytes: Lymphocytes

The ratio of monocytes and lymphocytes (ML ratio) in peripheral blood is associated with tuberculosis and malaria disease risk and cancer and cardiovascular disease outcomes. We studied anti-mycobacterial function and the transcriptome of monocytes in relation to the ML ratio.

Mycobacterial growth inhibition assays of whole or sorted blood were performed and mycobacteria were enumerated by liquid culture. Transcriptomes of unstimulated CD14 + monocytes isolated by magnetic bead sorting were characterised by microarray. Transcript expression was tested for association with ML ratio calculated from leucocyte differential counts by linear regression.

The ML ratio was associated with mycobacterial growth in vitro (β = 2.23, SE 0.91, p = 0.02). Using sorted monocytes and lymphocytes, in vivo ML ratio (% variance explained R² = 11%, p = 0.02) dominated over in vitro ratios (R² = 5%, p = 0.10) in explaining mycobacterial growth. Expression of 906 genes was associated with the ML ratio and 53 with monocyte count alone. ML-ratio associated genes were enriched for type-I and -II interferon signalling (p = 1.2 × 10^− 8), and for genes under transcriptional control of IRF1, IRF2, RUNX1, RELA and ESRRB. The ML-ratio-associated gene set was enriched in TB disease (3.11-fold, 95% CI: 2.28–4.19, p = 5.7 × 10^− 12) and other inflammatory diseases including atopy, HIV, IBD and SLE.

The ML ratio is associated with distinct transcriptional and anti-mycobacterial profiles of monocytes that may explain the disease associations of the ML ratio.

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A pathophysiological basis for involvement of the ML ratio in infectious, malignant and cardiovascular diseases is unclear.

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Monocytes from individuals with high ML ratio have impaired control of mycobacterial growth and a distinctive transcriptome.

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These monocytes are characterised by enhanced interferon signalling, and intermediate transcription factors.

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The ML-ratio associated transcript signature is enriched in TB and other diseases including atopy, IBD and SLE.

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Ontogeny-specific function of monocytes may be the possible mechanism for the prognostic value of the ML ratio.

Enumeration of the absolute count of white blood cell subsets is one of the most frequently performed tests in clinical practice. Recently, elevation in the monocytes:lymphocytes (ML) ratio was linked to increased risk of tuberculosis and malaria disease, and poorer outcomes for many cancers and cardiovascular diseases. We sought to understand the mechanism of these disease associations. We found that the ML ratio reflects the functional capacity of monocytes and that genes that are differentially expressed in monocytes from donors with a high ML ratio are similar to those in other diseases such as HIV and inflammatory bowel disease. Because a specific type of blood-making stem cell regulates the ML ratio, it is plausible that the ratio reflects monocyte function because it is a clue to different monocyte origins. Our findings offer a mechanism for the predictive value of the ML ratio that may help improve its clinical utility.

The Ikaros family of zinc-finger proteins

Ikaros represents a zinc-finger protein family important for lymphocyte development and certain other physiological processes. The number of family members is large, with alternative splicing producing various additional isoforms from each of the five homologous genes in the family. The functional forms of Ikaros proteins could be even more diverse due to protein–protein interactions readily established between family members. Emerging evidence suggests that targeting Ikaros proteins is feasible and effective in therapeutic applications, although the exact roles of Ikaros proteins remain elusive within the intricate regulatory networks in which they are involved. In this review we collect existing knowledge as to the functions, regulatory pathways, and molecular mechanisms of this family of proteins in an attempt to gain a better understanding through the comparison of activities and interactions among family members.

A Phase II Clinical Trial of TRC105 (Anti-Endoglin Antibody) in Adults With Advanced/Metastatic Urothelial Carcinoma

BACKGROUND

In this trial we assessed the efficacy and tolerability of TRC105, a chimeric monoclonal antibody that targets CD105 (endoglin) in patients with advanced, previously treated urothelial carcinoma (UC).

PATIENTS AND METHODS

Patients received TRC105 15 mg/kg every 2 weeks on days 1 and 15 of each 28-day cycle. The primary end point was progression-free survival (PFS) at 6 months. Secondary end points included safety, toxicity, and overall survival (OS). CD105 expression was evaluated using immunohistochemistry (IHC) in a separate cohort of 50 UC patients. Biomarker studies included immune subsets, circulating tumor cells (CTCs), circulating endothelial cells (CECs), circulating endothelial progenitor cells (CEPs), and osteopontin.

RESULTS

Of 13 patients enrolled, 12 were evaluable for OS and PFS. The 3-month PFS probability was 18.2% (median PFS, 1.9 months [95% confidence interval (CI), 1.8-2.1 months). This met the criterion for ending accrual on the basis of the 2-stage design. Median OS was 8.3 months (95% CI, 3.3-17.0 months). IHC for CD105 scores was not associated with T stage (P = .26) or presence of lymph nodes (P = .64). Baseline levels of regulatory T and B cells, CEPs, and changes in CEC level after TRC105 exhibited trends toward an association with PFS or OS. CTCs pre- and post-TRC105 were detected in 4 of 4 patients.

CONCLUSION

Although TRC105 was well tolerated, it did not improve 6-month PFS in heavily pretreated patients with advanced UC. CD105 staining was present in 50% of UC tumors at different intensities. Our observations on the pharmacodynamic significance of immune subsets, CECs, and CTCs warrant further study.

Imbalanced immune homeostasis in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder resulting from low platelet counts caused by inadequate production as well as increased destruction by autoimmune mechanisms. As with other autoimmune disorders, chronic ITP is characterized by perturbations of immune homeostasis with hyperactivated effector cells as well as defective regulatory arm of the adaptive immune system, which will be reviewed here. Interestingly, some ITP treatments are associated with restoring the regulatory imbalance, although it remains unclear whether the immune system is redirected to a state of tolerance once treatment is discontinued. Understanding the mechanisms that result in breakdown of immune homeostasis in ITP will help to identify novel pathways for restoring tolerance and inhibiting effector cell responses. This information can then be translated into developing therapies for averting autoimmunity not only in ITP but also many autoimmune disorders.

The Interplay Between Monocytes/Macrophages and CD4(+) T Cell Subsets in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by inflammation of the synovial lining (synovitis). The inflammation in the RA joint is associated with and driven by immune cell infiltration, synovial hyperproliferation, and excessive production of proinflammatory mediators, such as tumor necrosis factor α (TNFα), interferon γ (IFNγ), interleukin (IL)-1β, IL-6, and IL-17, eventually resulting in damage to the cartilage and underlying bone. The RA joint harbors a wide range of immune cell types, including monocytes, macrophages, and CD4(+) T cells (both proinflammatory and regulatory). The interplay between CD14(+) myeloid cells and CD4(+) T cells can significantly influence CD4(+) T cell function, and conversely, effector vs. regulatory CD4(+) T cell subsets can exert profound effects on monocyte/macrophage function. In this review, we will discuss how the interplay between CD4(+) T cells and monocytes/macrophages may contribute to the immunopathology of RA.

Blocking of LFA-1 enhances expansion of Th17 cells induced by human CD14(+) CD16(++) nonclassical monocytes

Among human peripheral blood (PB) monocyte (Mo) subsets, the classical CD14(++) CD16(-) (cMo) and intermediate CD14(++) CD16(+) (iMo) Mos are known to activate pathogenic Th17 responses, whereas the impact of nonclassical CD14(+) CD16(++) Mo (nMo) on T-cell activation has been largely neglected. The aim of this study was to obtain new mechanistic insights on the capacity of Mo subsets from healthy donors (HDs) to activate IL-17(+) T-cell responses in vitro, and assess whether this function was maintained or lost in states of chronic inflammation. When cocultured with autologous CD4(+) T cells in the absence of TLR-2/NOD2 agonists, PB nMos from HDs were more efficient stimulators of IL-17-producing T cells, as compared to cMo. These results could not be explained by differences in Mo lifespan and cytokine profiles. Notably, however, the blocking of LFA-1/ICAM-1 interaction resulted in a significant increase in the percentage of IL-17(+) T cells expanded in nMo/T-cell cocultures. As compared to HD, PB Mo subsets of patients with rheumatoid arthritis were hampered in their T-cell stimulatory capacity. Our new insights highlight the role of Mo subsets in modulating inflammatory T-cell responses and suggest that nMo could become a critical therapeutic target against IL-17-mediated inflammatory diseases.

In vitro TNF blockade enhances ex vivo expansion of regulatory T cells in patients with immune thrombocytopenia

Tumour necrosis factor-α (TNF) is an inflammatory cytokine that is elevated in a number of autoimmune diseases including immune thrombocytopenia (ITP), a bleeding disorder characterized by low platelet counts. In vitro TNF blockade increases expansion of the regulatory T cell (Treg) IKZF2 (also termed Helios) subset in T cell-monocyte cocultures from healthy donors, but its role on proliferative responses of Tregs in ITP patients, who have altered immunoregulatory compartment, remains unclear. TNF in CD4+ T cells from patients with chronic ITP were elevated and negatively correlated with peripheral Treg frequencies, suggesting a possible inhibitory effect of TNF on ITP Tregs. In vitro antibody neutralization with anti-TNF in T cell-monocyte cocultures resulted in a robust expansion of pre-existing ITP Tregs, higher than in healthy controls. Similar to the effects of anti-TNF antibodies, TNF blockade with antibodies against TNFRSF1B (anti-TNFRSF1B, previously termed anti-TNFRII) almost doubled ITP Treg expansion whereas neutralization with anti-TNFRSF1A (anti-TNFRI) antibodies had no effect on proliferative responses of Tregs. In addition, TNFRSF1B levels on ITP Tregs were significantly elevated, which may explain the increased susceptibility of patient Tregs to the actions of TNF blockade. Altogether, these data raise the possibility that TNF blockers, through their ability to increase Treg proliferation, may be efficacious in ITP patients.

IL-33 is an unconventional Alarmin that stimulates IL-2 secretion by dendritic cells to selectively expand IL-33R/ST2+ regulatory T cells

IL-33 is a recently characterized IL-1 family member that is proposed to function as an alarmin, or endogenous signal of cellular damage, as well as act as a pleiotropic cytokine. The ability of IL-33 to potentiate both Th1 and Th2 immunity supports its role in pathogen clearance and disease immunopathology. Yet, IL-33 restrains experimental colitis and transplant rejection by expanding regulatory T cells (Treg) via an undefined mechanism. We sought to determine the influence of IL-33 on hematopoietic cells that drives Treg expansion and underlies the therapeutic benefit of IL-33 administration. In this study, we identify a feedback loop in which conventional mouse CD11c(+) dendritic cells (DC) stimulated by IL-33 secrete IL-2 to selectively expand IL-33R(ST2(+))- suppressive CD4(+)Foxp3(+) Treg. Interestingly, this occurs in the absence of classical DC maturation, and DC-derived (innate) IL-2 increases ST2 expression on both DC and interacting Treg. ST2(+) Treg represent an activated subset of Foxp3(+) cells, demonstrated to be ICOS(high)CD44(high) compared with their ST2(-) counterparts. Furthermore, although studies have shown that IL-33-exposed DC promote Th2 responses, we reveal that ST2(+) DC are required for IL-33-mediated in vitro and in vivo Treg expansion. Thus, we have uncovered a relationship between IL-33 and innate IL-2 that promotes the selective expansion of ST2(+) Treg over non-Treg. These findings identify a novel regulatory pathway driven by IL-33 in immune cells that may be harnessed for therapeutic benefit or for robust expansion of Treg in vitro and in vivo.

'Hardcore' OX40+ immunosuppressive regulatory T cells in hepatic cirrhosis and cancer

Human regulatory T cells (Tregs) comprise an array of distinct subsets displaying diverse functions in response to microenvironmental signals. Here, we review our recent findings demonstrating the preferential accumulation of uncommitted, Th1-like and OX40^- Tregs in non-cirrhotic tissues in contrast to the presence of committed, Th1-suppressing and OX40⁺ Tregs in cirrhotic and tumor contexts in human liver affected by chronic hepatitis C.

EFFECT OF LIPOSOMAL CLODRONATE-DEPENDENT DEPLETION OF PROFESSIONAL ANTIGEN PRESENTING CELLS ON NUMBERS AND PHENOTYPE OF CANINE CD4+CD25+FOXP3+ REGULATORY T CELLS

Regulatory T cells (Tregs) are known to control autoreactivity during and subsequent to the development of the peripheral immune system. Professional antigen presenting cells (APCs), dendritic cells (DCs) and monocytes, have an important role in inducing Tregs. For the first time, this study evaluated proportions and phenotypes of Tregs in canine peripheral blood depleted of professional APCs, utilizing liposomal clodronate (LC) and multicolor flow cytometry analysis. Our results demonstrate that LC exposure promoted short term decreases followed by significant increases in the proportions or absolute numbers of CD4⁺CD25⁺FOXP3⁺ Tregs in dogs. In general, the LC-dependent Treg fluctuations were similar to the changes in the levels of CD14⁺ monocytes in Walker hounds. However, the proportions of monocytes showed more dramatic changes compared to the proportions of Tregs that were visually unchanged after LC treatment over the study period. At the same time, absolute Treg numbers showed, similarly to the levels of CD14⁺ monocytes, significant compensatory gains as well as the recovery during the normalization period. We confirm the previous data that CD4⁺ T cells with the highest CD25 expression were highly enriched for FOXP3. Furthermore, for the first time, we report that CD4⁺CD25^lowFOXP3⁺ is the major regulatory T cell subset affected by LC exposure. The increases within the lowest CD25 expressers of CD4⁺FOXP3⁺ cells together with compensatory gains in the proportion of CD14⁺ monocytes during compensatory and normalization periods suggest the possible direct or indirect roles of monocytes in active recruitment and generation of Tregs from naïve CD4⁺ T cells.

Hemin controls T cell polarization in sickle cell alloimmunization

Patients with sickle cell disease (SCD) often require transfusions to treat and prevent worsening anemia and other SCD complications. However, transfusions can trigger alloimmunization against transfused RBCs with serious clinical sequelae. Risk factors for alloimmunization in SCD remain poorly understood. We recently reported altered regulatory T cell (Treg) and Th responses with higher circulating Th1 (IFN-γ(+)) cytokines in chronically transfused SCD patients with alloantibodies as compared with those without alloantibodies. Because monocytes play a critical role in polarization of T cell subsets and participate in clearance of transfused RBCs, we tested the hypothesis that in response to the RBC breakdown product hemin, monocyte control of T cell polarization will differ between alloimmunized and non-alloimmunized SCD patients. Exogenous hemin induced Treg polarization in purified T cell/monocyte cocultures from healthy volunteers through the monocyte anti-inflammatory heme-degrading enzyme heme oxygenase-1. Importantly, hemin primarily through its effect on CD16+ monocytes induced an anti-inflammatory (higher Treg/lower Th1) polarization state in the non-alloimmunized SCD group, whereas it had little effect in the alloimmunized group. Non-alloimmunized SCD CD16+ monocytes expressed higher basal levels of heme oxygenase-1. Furthermore, IL-12, which contributed to a proinflammatory polarization state (low Treg/high Th1) in SCD, was dampened in hemin-treated stimulated monocytes from non-alloimmunized SCD patients, but not in the alloimmunized group. These data suggest that unlike alloimmunized patients, non-alloimmunized SCD CD16+ monocytes in response to transfused RBC breakdown products promote an anti-inflammatory state that is less conducive to alloimmunization.

Targeting monocyte and macrophage subpopulations for immunotherapy: a patent review (2009 - 2013)

INTRODUCTION

Monocytes and macrophages are heterogeneous populations of effector cells in the innate immune system. Once thought to be obligatory precursors for macrophages, monocytes are now known to have several distinct sub-populations and their own independent functions. This separation of the two lineages has opened new therapeutic avenues in inflammation and created new technologies targeting the mononuclear phagocyte system (MPS).

AREAS COVERED

A search of Google Patents and PatentScope has revealed numerous patents targeting monocytes and macrophages. This review will focus on seven patents from 2009 to 2013, utilizing autologous monocyte and macrophage adoptive transfer, genetic manipulation of the MPS, therapeutic nanoparticles and liposomes or combinations of these strategies. Patents that target monocyte recruitment are also briefly reviewed.

EXPERT OPINION

While monocyte and macrophage targeting has yielded some promising results in animal models, these often fail to translate well to successful clinical trials. The paradigm of how cells in the MPS interact and evolve is constantly being updated, and caution must be exercised in developing immunomodulatory agents until this relationship is better understood.

Peripheral and thymic foxp3(+) regulatory T cells in search of origin, distinction, and function

Over the past decade, much has been learnt and much more to discover about Foxp3(+) regulatory T cells (Tregs). Initially, it was thought that Tregs were a unique entity that originates in the thymus. It is now recognized that there is a fraternal twin sibling that is generated in the periphery. The difficulty is in the distinction between these two subsets. The ability to detect, monitor, and analyze these two subsets in health and disease will provide invaluable insights into their functions and purposes. The plasticity and mechanisms of action can be unique and not overlapping within these subsets. Therefore, the therapeutic targeting of a particular subset of Tregs might be more efficacious. In the past couple of years, a vast amount of data have provided a better understanding of the cellular and molecular components essential for their development and stability. Many studies are implicating their preferential involvement in certain diseases and immunologic tolerance. However, it remains controversial as to whether any phenotypic markers have been identified that can differentiate thymic versus peripheral Tregs. This review will address the validity and controversy regarding Helios, Lap/Garp and Neuropilin-1 as markers of thymic Tregs. It also will discuss updated information on distinguishing features of these two subsets and their critical roles in maternal-fetal tolerance and transplantation.