Plasticity of T(reg) cells: is reprogramming of T(reg) cells possible in the presence of FOXP3?

Transient Foxp3(+) regulatory T-cell depletion enhances protective Th1/Th17 immune response in murine sporotrichosis caused by Sporothrix schenckii

The role of regulatory T cells (Tregs) on protective immunity in fungal infections, is controversial. Sporotrichosis is an emerging and worldwide-distributed subcutaneous mycosis caused by various related thermodimorphic fungi of the genus Sporothrix. Previously, we showed an elevated percent of Tregs around 21 days post-infection (dpi) in C57BL/6 mice infected with either Sporothrix schenckii or Sporothrix brasiliensis, but the effect of these cells in the ongoing infection was not evaluated. Here, we aim to characterize the role of Foxp3+ Tregs in a subcutaneous S. schenckii infection model. The flow cytometric analyses showed that S. schenckii infection elicited an expansion of a splenic CD4+Foxp3+ population, including a subset of Helios^low+ after ex vivo stimulation with S. schenckii-heat killed yeast. Depletion of Tregs in DEREG mice revealed a reduction of fungal burden in the skin and systemically in liver and kidneys, associated with enhanced Th1 and Th17 responses. Altogether, our results reveal for the first time that Tregs depletion in ongoing S. schenckii infection improves the protective antifungal immunity and these data suggest that Tregs modulation could be explored as a potential therapeutic strategy in sporotrichosis.

CRISPR screen in regulatory T cells reveals modulators of Foxp3

Regulatory T cells (Tregs) are required to control immune responses and maintain homeostasis, but are a significant barrier to anti-tumor immunity¹. Conversely, Treg instability, characterized by loss of the master transcription factor Foxp3 and acquisition of pro-inflammatory properties², can promote autoimmunity and/or facilitate more effective tumor immunity^3,4. A comprehensive understanding of the pathways that regulate Foxp3 could lead to more effective Treg therapies for autoimmune disease and cancer. Despite improved functional genetic tools that now allow for systematic interrogation, dissection of the gene regulatory programs that modulate Foxp3 expression has not yet been reported. In this study, we developed a CRISPR-based pooled screening platform for phenotypes in primary mouse Tregs and applied this technology to perform a targeted loss-of-function screen of ~490 nuclear factors to identify gene regulatory programs that promote or disrupt Foxp3 expression. We discovered several novel modulators including ubiquitin-specific peptidase 22 (Usp22) and ring finger protein 20 (Rnf20). Usp22, a member of the deubiquitination module of the SAGA chromatin modifying complex, was discovered to be a positive regulator that stabilized Foxp3 expression; whereas the screen suggested Rnf20, an E3 ubiquitin ligase, can serve as a negative regulator of Foxp3. Treg-specific ablation of Usp22 in mice reduced Foxp3 protein and created defects in their suppressive function that led to spontaneous autoimmunity but protected against tumor growth in multiple cancer models. Foxp3 destabilization in Usp22-deficient Tregs could be rescued by ablation of Rnf20, revealing a reciprocal ubiquitin switch in Tregs. These results reveal novel modulators of Foxp3 and demonstrate a screening method that can be broadly applied to discover new targets for Treg immunotherapies for cancer and autoimmune disease.

Low expression and hypermethylation of FOXP3 in regulatory T cells are associated with asthma in children

The aim of the present study was to determine the expression and methylation levels of forkhead transcription factor P3 (FOXP3) in peripheral blood CD4⁺CD25⁺ regulatory T cells (Tregs) harvested from children with asthma, and to explore the pathogenesis of asthma. The percentages of CD4⁺CD25⁺FOXP3⁺ Tregs in CD4⁺ T lymphocytes from 15 children with asthma and 15 healthy controls were measured by flow cytometry, and FOXP3 mRNA expression in the CD4⁺CD25⁺ Tregs was measured by reverse transcriptase-quantitative PCR. In addition, the forced expiratory volume in one second (FEV1) was measured to determine lung function. The methylation statuses of 16 CpG sites in two regions of the FOXP3 gene's exon and intron were analysed with bisulfite-specific PCR and pyrophosphate sequencing. The differences in methylation levels between the asthma and control groups were compared. The percentage of CD4⁺CD25⁺FOXP3⁺ Tregs in CD4⁺ T lymphocytes and FOXP3 mRNA expression were significantly lower in children with asthma than in control children (P<0.05). The FOXP3 mRNA levels in children with asthma were positively correlated with FEV1 (P<0.001; r=0.895). The methylation levels in 12 of the 16 studied CpG loci of the FOXP3 gene, and of the 6th CpG locus in the exon regions, were significantly higher in the asthma group compared with the control group (P<0.05). In summary, low expression and hypermethylation of the FOXP3 gene in the peripheral blood were associated with the pathogenesis of asthma in children. Thus, the FOXP3 mRNA expression level can be used to predict the severity of asthma in children.

Naturally occurring tolerance acquisition to foods in previously allergic children is characterized by antigen specificity and associated with increased subsets of regulatory T cells

BACKGROUND

Food allergy affects approximately 6-8% of children, and increasing in prevalence. Some children naturally outgrow their food allergy without intervention, but the mechanisms by which this occurs remain poorly understood. We sought to investigate the role of regulatory T cells in the development of naturally acquired tolerance.

METHODS

Fifty-eight children (1-18 years) with either egg or peanut allergy, recent acquisition of natural tolerance to egg or peanut, or no food allergy were studied. Peripheral blood mononuclear cells (PBMC) from these groups were stimulated with relevant antigen for 48 h and flow cytometry performed to characterize both surface (CD3, CD4, CD25, CD14, CD19, and CD127) and intracellular markers (IL-10, Foxp3, and IL-5).

RESULTS

Resting PBMC from naturally tolerant patients had significantly increased CD3+CD4+CD25+CD127loFoxp3+ cells, when compared to allergic or control patients (mean 6.36 vs. 2.37 vs. 2.62%, respectively, P < 0.05). Upon stimulation with relevant antigen, naturally tolerant patients also had increased IL-10-expressing CD25+CD127lo cells (6.33 vs. 1.65 vs. 0.7, P < 0.01), Foxp3+ cells (mean 12.6 vs. 5.42 vs. 3%, P < 0.01), and CD4+ cells (mean 4.48 vs. 1.59 vs. 0.87%, P < 0.01); the increase was not observed in PBMCs from allergic or control patients. Additionally, this upregulation was only seen with relevant antigen stimulation and not upon stimulation with unrelated antigen.

CONCLUSION

The increased CD3+CD4+CD25+CD127lo cells at baseline and upon stimulation and increased induction of IL-10-producing cells of several types, including Tr1 cells, from naturally tolerant patients suggests an important role for regulatory T cell subsets in the acquisition of natural tolerance.

Restoring homeostasis of CD4+ T cells in hepatitis-B-virus-related liver fibrosis

Immune-mediated liver injury is widely seen during hepatitis B virus (HBV) infection. Unsuccessful immune clearance of HBV results in chronic hepatitis and increases the risk of liver cirrhosis and hepatocellular carcinoma. HBV-related liver fibrosis (HBVLF), occurring as a result of HBV-induced chronic hepatitis, is a reversible, intermediate stage of chronic hepatitis B (CHB) and liver cirrhosis. Therefore, defining the pathogenesis of HBVLF is of practical significance for achieving better clinical outcomes. Recently, the homeostasis of CD4⁺ T cells was considered to be pivotal in the process of HBVLF. To better uncover the underlying mechanisms, in this review, we systematically retrospect the impacts of different CD4⁺ T-cell subsets on CHB and HBVLF. We emphasize CD4⁺ T-cell homeostasis and the important balance between regulatory T (Treg) and T helper 17 (Th17) cells. We discuss some cytokines associated with Treg and Th17 cells such as interleukin (IL)-17, IL-22, IL-21, IL-23, IL-10, IL-35 and IL-33, as well as surface molecules such as programmed cell death protein 1, cytotoxic T lymphocyte-associated antigen 4, T cell immunoglobulin domain and mucin domain-containing molecule 3 and cannabinoid receptor 2 that have potential therapeutic implications for the homeostasis of CD4⁺ T cells in CHB and HBVLF.

Toll-like receptors, immunoproteasome and regulatory T cells in children with Henoch-Schönlein purpura and primary IgA nephropathy

BACKGROUND

Henoch-Schönlein purpura (HSP) nephritis and primary IgA nephropathy (pIgAN) present with glomerular IgA deposits, but differ with regard to clinical features. The suspected involvement of different immune system pathways is largely unknown.

METHODS

This study was aimed at investigating some of the immunological features including Toll-like receptors (TLR), proteasome (PS)/immunoproteasome (iPS) switch, and the regulatory T cell system (Treg/Th17 cells) in 63 children with HSP with/without renal involvement and in 25 with pIgAN. Real-time PRC (Taqman) was used to quantify mRNA levels in peripheral blood mononuclear cells (PBMC).

RESULTS

The expression of mRNAs encoding for TLR4 in both HSP and pIgAN was higher than in controls (HC) and in both diseases FoxP3mRNA and TGF-β1mRNA expression was significantly lower than in HC. A switch from PS to iPS (LMP2/β1) was detected only in PBMC of HSP and it correlated with the level of TLR2mRNA, which was selectively increased only in children with HSP.

CONCLUSION

Children with HSP and pIgAN present with similar signs of engagement of the innate immunity and regulatory T cell depression. The increased immunoproteasome switch, which correlated with TLR2 activation, may suggest an innate immunity pathway peculiar to HSP vasculitic presentation. This research area also deserves further investigation for possible therapeutic applications.

MiRNome and transcriptome aided pathway analysis in human regulatory T cells

Owing to their manifold immune regulatory functions, regulatory T cells (Treg) have received tremendous interest as targets for therapeutic intervention of diverse immunological pathologies or cancer. Directed manipulation of Treg will only be achievable with extensive knowledge about the intrinsic programs that define their regulatory function. We simultaneously analyzed miR and mRNA transcript levels in resting and activated human Treg cells in comparison with non-regulatory conventional T cells (Tcon). Based on experimentally validated miR-target information, both transcript levels were integrated into a comprehensive pathway analysis. This strategy revealed characteristic signal transduction pathways involved in Treg biology such as T-cell receptor-, Toll-like receptor-, transforming growth factor-β-, JAK/STAT (Janus kinase/signal transducers and activators of transcription)- and mammalian target of rapamycin signaling, and allowed for the prediction of specific pathway activities on the basis of miR and mRNA transcript levels in a probabilistic manner. These data encourage new concepts for targeted control of Treg cell effector functions.

Mast cell-derived serine proteinase regulates T helper 2 polarization

Although mast cells play a critical role in allergic reactions, the cells are also involved in the protective immunity in the body. This study aims to investigate the role of mast cells in immune regulation during aberrant T helper (Th)2 responses. In this study, an adoptive antigen-specific Th2 response model was established with mast cell-deficient mice to test the role of mast cell in the immune regulation. Cell culture was employed to test the role of mast cells in the modulation of the expression of B cell lymphoma 6 protein (Bcl-6) in Th2 cells. The results showed that after adoptive transfer with immune cells, the mast cell-deficient mice showed stronger Th2 pattern responses in the intestine than that in the mast cell-sufficient mice. Mast cell-derived mouse mast cell protease-6 increased the expression of Bcl-6 in Th2 cells. Bcl-6 inhibited the expression of GATA-3 in Th2 cells, subsequently, forkhead box P3 was increased and the Th2 cytokines were reduced in the cells; the cells thus showed the immune regulatory properties similar to regulatory T cells. We conclude that bedsides initiating immune inflammation, mast cells also contribute to the immune regulation on Th2 polarization.

Measurement of suppressor activity of T CD4⁺CD25⁺ T reg cells using bromodeoxyuridine incorporation assay

The suppressor effect of T regulatory lymphocytes in co-cultures with T effector cells obtained by magnetic columns from healthy donors and activated by CD3/CD28 was measured by a proliferation assay using BrdU incorporation and an ELISA test. Tritiated thymidine incorporation was used as a reference since it is the gold standard for proliferation assays. Both methods were used simultaneously in the same samples in order to compare them. Correlation between them was statistically significant (p < 0.001). The purification using magnetic columns was very efficient since CD4⁺CD25⁺ cells were also FOXP3⁺ therefore; they were identified as suppressor T cells. The use of BrdU incorporation in suppression assays is an excellent method that avoids the use of radioactive contaminating materials.

Comparative approach to define increased regulatory T cells in different cancer subtypes by combined assessment of CD127 and FOXP3

In recent years an increase of functional CD4⁺CD25⁺ regulatory T cells (T_reg cells) has been established for patients with solid tumors, acute leukemias, and lymphomas. We have reported an expanded pool of CD4⁺CD25^high T_reg cells in patients with chronic lymphatic leukemia (CLL), multiple myeloma (MM) as well as its premalignant precursor monoclonal gammopathy of undetermined significance (MGUS). In healthy individuals, low-level expression of CD127 on T cells in addition to the expression of FOXP3 has been associated with T_reg cells. Here, we demonstrate that the expanded FOXP3⁺ T-cell population in patients with colorectal cancer, CLL, MGUS, MM, follicular lymphoma, and Hodgkin's disease are exclusively CD127^low T_reg cells and were strongly suppressive. A significant portion of CD127^lowFOXP3⁺ T_reg cells expressed only low levels of CD25 suggesting that the previously reported expansion of CD25⁺ T_reg cells underestimates the true expansion. The assessment of CCR7 and CD45RA expression on the expanded CD4⁺CD127^lowFOXP3⁺ T_reg cells revealed an increase of both naïve as well as central and effector memory T_reg cells in peripheral blood. Our data strongly support superiority of combined CD127 and FOXP3 analysis in comparison to CD25 and FOXP3 assessment for further quantification of T_reg cells in malignant diseases.