Human Regulatory T Cells: Understanding the Role of Tregs in Select Autoimmune Skin Diseases and Post-Transplant Nonmelanoma Skin Cancers

Regulatory T cells (Tregs) play an important role in maintaining immune tolerance and homeostasis by modulating how the immune system is activated. Several studies have documented the critical role of Tregs in suppressing the functions of effector T cells and antigen-presenting cells. Under certain conditions, Tregs can lose their suppressive capability, leading to a compromised immune system. For example, mutations in the Treg transcription factor, Forkhead box P3 (FOXP3), can drive the development of autoimmune diseases in multiple organs within the body. Furthermore, mutations leading to a reduction in the numbers of Tregs or a change in their function facilitate autoimmunity, whereas an overabundance can inhibit anti-tumor and anti-pathogen immunity. This review discusses the characteristics of Tregs and their mechanism of action in select autoimmune skin diseases, transplantation, and skin cancer. We also examine the potential of Tregs-based cellular therapies in autoimmunity.

The dichotomous outcomes of TNFα signaling in CD4+ T cells

TNFa blocking agents were the first-in-class biologic drugs used for the treatment of autoimmune disease. Paradoxically, however, exacerbation of autoimmunity was observed in some patients. TNFa is a pleiotropic cytokine that has both proinflammatory and regulatory effects on CD4+ T cells and can influence the adaptive immune response against autoantigens. Here, we critically appraise the literature and discuss the intricacies of TNFa signaling that may explain the controversial findings of previous studies. The pleiotropism of TNFa is based in part on the existence of two biologically active forms of TNFa, soluble and membrane-bound, with different affinities for two distinct TNF receptors, TNFR1 and TNFR2, leading to activation of diverse downstream molecular pathways involved in cell fate decisions and immune function. Distinct membrane expression patterns of TNF receptors by CD4+ T cell subsets and their preferential binding of distinct forms of TNFα produced by a diverse pool of cellular sources during different stages of an immune response are important determinants of the differential outcomes of TNFa-TNF receptor signaling. Targeted manipulation of TNFa-TNF receptor signaling on select CD4+ T cell subsets may offer specific therapeutic interventions to dampen inflammation while fortifying immune regulation for the treatment of autoimmune diseases.

p53 Activation Effect in the Balance of T Regulatory and Effector Cell Subsets in Patients With Thyroid Cancer and Autoimmunity

Carcinomas evade the host immune system by negatively modulating CD4+ and CD8+ T effector lymphocytes through forkhead box protein 3 (FOXP3) positive T regulatory cells’ increased activity. Furthermore, interaction of the programmed cell death 1 (PD1) molecule and its ligand programmed cell death ligand 1 (PDL1) inhibits the antitumor activity of PD1+ T lymphocytes. Immunotherapy has become a powerful strategy for tailored cancer patients’ treatment both in adult and pediatric patients aiming to generate potent antitumor responses. Nevertheless, immunotherapies can generate autoimmune responses. This study aimed to investigate the potential effect of the transformation-related protein 53 (p53) reactivation by a peptide-based inhibitor of the MDM2/MDM4 heterodimer (Pep3) on the immune response in a solid cancer, i.e., thyroid carcinoma frequently presenting with thyroid autoimmunity. In peripheral blood mononuclear cell of thyroid cancer patients, Pep3 treatment alters percentages of CD8+ and CD4+ T regulatory and CD8+ and CD4+ T effector cells and favors an anticancer immune response. Of note that reduced frequencies of activated CD8+ and CD4+ T effector cells do not support autoimmunity progression. In evaluating PD1 expression under p53 activation, a significant decrease of activated CD4+PD1+ cells was detected in thyroid cancer patients, suggesting a defective regulation in the initial activation stage, therefore generating a protective condition toward autoimmune progression.

Regulation of autoreactive CD4 T cells by FoxO1 signaling in CNS autoimmunity

Myelin-specific CD4 T effector cells (Teffs), Th1 and Th17 cells, are encephalitogenic in experimental autoimmune encephalomyelitis (EAE), a well-defined murine model of multiple sclerosis (MS) and implicated in MS pathogenesis. Forkhead box O 1 (FoxO1) is a conserved effector molecule in PI3K/Akt signaling and critical in the differentiation of CD4 T cells into T helper subsets. However, it is unclear whether FoxO1 may be a target for redirecting CD4 T cell differentiation and benefit CNS autoimmunity. Using a selective FoxO1 inhibitor AS1842856, we show that inhibition of FoxO1 suppressed the differentiation and expansion of Th1 cells. The transdifferentiation of Th17 cells into encephalitogenic Th1-like cells was suppressed by FoxO1 inhibition upon reactivation of myelin-specific CD4 T cells from EAE mice. The transcriptional balance skewed from the Th1 transcription factor T-bet toward the Treg transcription factor Foxp3. Myelin-specific CD4 T cells treated with the FoxO1 inhibitor were less encephalitogenic in adoptive transfer EAE studies. Inhibition of FoxO1 in T cells from MS patients significantly suppressed the expansion of Th1 cells. Furthermore, FoxO1 inhibition with AS1842856 promoted the development of functional iTreg cells. The immune checkpoint programmed cell death protein-1 (PD-1)-induced Foxp3 expression in CD4 T cells was impaired by FoxO1 inhibition. These data illustrate an important role of FoxO1 signaling in CNS autoimmunity via regulating autoreactive Teff and Treg balance.

Sustained IL-2R signaling of limited duration by high-dose mIL-2/mCD25 fusion protein amplifies tumor-reactive CD8+ T cells to enhance antitumor immunity

High-dose IL-2 induces cancer regression but its therapeutic use is limited due to high toxicities resulting from its broad cell targeting. In one strategy to overcome this limitation, IL-2 has been modified to selectively target the intermediate affinity IL-2R that broadly activates memory-phenotypic CD8⁺ T and NK cells, while minimizing Treg-associated tolerance. In this study, we modeled an alternative strategy to amplify tumor antigen-specific TCR transgenic CD8⁺ T cells through limited application of a long-acting IL-2 fusion protein, mIL-2/mCD25, which selectively targets the high-affinity IL-2R. Here, mice were vaccinated with a tumor antigen and high-dose mIL-2/mCD25 was applied to coincide with the induction of the high affinity IL-2R on tumor-specific T cells. A single high dose of mIL-2/mCD25, but not an equivalent amount of IL-2, amplified the frequency and function of tumor-reactive CD8⁺ T effector (Teff) and memory cells. These mIL-2/mCD25-dependent effects relied on distinctive requirements for TLR signals during priming of CD8⁺ tumor-specific T cells. The mIL-2/mCD25-amplified tumor-reactive effector and memory T cells supported long-lasting antitumor responses to B16-F10 melanoma. This regimen only transiently increased Tregs, yielding a favorable Teff-Treg ratio within the tumor microenvironment. Notably, mIL-2/mCD25 did not increase non-tumor-specific Teff or NK cells within tumors, further substantiating the specificity of mIL-2/mCD25 for tumor antigen-activated T cells. Thus, the selectivity and persistence of mIL-2/mCD25 in conjunction with a tumor vaccine supports antitumor immunity through a mechanism that is distinct from recombinant IL-2 or IL-2-based biologics that target the intermediate affinity IL-2R.

Th1 concomitant immune response mediated by IFN-γ protects against sand fly delivered Leishmania infection: Implications for vaccine design

Leishmaniasis is an unresolved global health problem with a high socio-economic impact. Data generated in mouse models has revealed that the Th1 response, with IL-12, IFN-γ, TNF-α, and IL-2 as prominent cytokines, predominantly controls the disease progression. Premised on these findings, all examined vaccine formulations have been aimed at generating a long-lived memory Th1 response. However, all vaccine formulations with the exception of live Leishmania inoculation (leishmanization) have failed to sufficiently protect against sand fly delivered infection. It has been recently unraveled that sand fly dependent factors may compromise pre-existing Th1 memory. Further scrutinizing the immune response after leishmanization has uncovered the prominent role of early (within hours) and robust IFN-γ production (Th1 concomitant immunity) in controlling the sand fly delivered secondary infection. The response is dependent upon parasite persistence and subclinical ongoing primary infection. The immune correlates of concomitant immunity (Resident Memory T cells and Effector T subsets) mitigate the early effects of sand fly delivered infection and help to control the disease. In this review, we have described the early events after sand fly challenge and the role of Th1 concomitant immunity in the protective immune response in leishmanized resistant mouse model, although leishmanization is under debate for human use. Undoubtedly, the lessons we learn from leishmanization must be further implemented in alternative vaccine approaches.

Selective deletion of Eos (Ikzf4) in T-regulatory cells leads to loss of suppressive function and development of systemic autoimmunity

Eos (lkzf4) is a member of the Ikaros family of transcription factors and is preferentially expressed in T-regulatory (Treg) cells. However, the role of Eos in Treg function is controversial. One study using siRNA knock down of Eos demonstrated that it was critical for Treg suppressor function. In contrast, Treg from mice with a global deficiency of Eos had normal Treg function in vitro and in vivo. To further dissect the function of Eos in Tregs, we generated mice with a conditional knock out of Eos in Treg cells (lkzf4fl/fl X Foxp3YFP-cre, Eos cKO). Deletion of Eos in Treg resulted in activation of CD4+Foxp3- and CD8+ T cells at the age of 3 months, cellular infiltration in non-lymphoid tissues, hyperglobulinemia, and anti-nuclear antibodies. While Tregs from Eos cKO mice displayed normal suppressive function in vitro, Eos cKO mice developed severe Experimental Autoimmune Encephalomyletis (EAE) following immunization with myelin oligodendrocyte glycoprotein (MOG) and Eos cKO Treg were unable to suppress Inflammatory Bowel Disease (IBD). Eos cKO mice had decreased growth of the transplantable murine adenocarcinoma MC38 tumor accompanied by enhanced IFN-γ/TNF-α production by CD8+ T cells in tumor draining lymph nodes. Mice with a global deficiency of Eos or a deficiency of Eos only in T cells developed autoimmunity at a much older age (12 months or 7-8 months, respectively). Taken together, Eos appears to play an essential role in multiple aspects of Treg suppressor function, but also plays an as yet unknown role in the function of CD4+Foxp3- and CD8+ T cells and potentially in non-T cells.

Direct Engagement of TLR9 Ligand with T Helper Cells Leads to Cell Proliferation & Up-regulation of Cytokines

PURPOSE

Toll like receptor (TLR) engagement is primarily a function of the innate immune cells. The purpose of the study was to assess direct uptake of ODN 2216 in T helper cells and effects on cell proliferation and cytokine expression.

METHODS

We isolated CD4+ CD25- T helper cells by magnetic sorting and studied the uptake of ODN 2216 using flow cytometry and confocal microscopy. We then studied the effect of ODN 2216 engagement on cell proliferation and cytokine expression using flow cytometry and gene expression of TLR9 signaling genes using real time RT-PCR.

RESULTS

We made a chance observation that purified T helper cells from healthy individuals consistently bind to the TLR9 ligand ODN 2216. In PBMCs, on the other hand, 98% of monocytes preferentially bound to ODN 2216 FITC, indicating that they competed with the lymphocytes. We confirmed intracellular localization of ODN 2216 FITC as well as intracellular expression of TLR9 in Thelper cells. Furthermore, ODN 2216 FITC was also co-localized with the lysosomal membrane associated protein 1. The uptake of TLR9 ligand culminated in cellular proliferation, up-regulation of cytokines and increased mRNA expression of TLR9 and IRF7 in T helper cells, in the absence of antigen presenting cells. ODN 2216 uptake was inhibited by promethazine as well as by TLR9 antagonist.

CONCLUSIONS

Our results show a direct engagement of TLR9 ligand in T helper cells and suggest involvement of TLR9 signalling in CD4+T cells, which may envisage novel targets for TLR inhibitors.

The IRF4 Gene Regulatory Module Functions as a Read-Write Integrator to Dynamically Coordinate T Helper Cell Fate

Transcriptional regulation during CD4⁺ T cell fate decisions enables their differentiation into distinct states, guiding immune responses toward antibody production via Tfh cells or inflammation by Teff cells. Tfh-Teff cell fate commitment is regulated by mutual antagonism between the transcription factors Bcl6 and Blimp-1. Here we examined how T cell receptor (TCR) signals establish and arbitrate Bcl6-Blimp-1 counter-antagonism. We found that the TCR-signal-induced transcription factor Irf4 is essential for the differentiation of Bcl6-expressing Tfh and Blimp-1-expressing Teff cells. Increased TCR signaling raised Irf4 amounts and promoted Teff cell fates at the expense of Tfh ones. Importantly, orthogonal induction of Irf4 expression redirected Tfh cell fate trajectories toward those of Teff. Mechanistically, we linked greater Irf4 abundance with its recruitment toward low-affinity binding sites within Teff cell cis-regulatory elements, including those of Prdm1. We propose that the Irf4 locus functions as the "reader" of TCR signal strength, and in turn, concentration-dependent activity of Irf4 "writes" T helper fate choice.

A mature macrophage is a principal HIV-1 cellular reservoir in humanized mice after treatment with long acting antiretroviral therapy

BACKGROUND

Despite improved clinical outcomes seen following antiretroviral therapy (ART), resting CD4+ T cells continue to harbor latent human immunodeficiency virus type one (HIV-1). However, such cells are not likely the solitary viral reservoir and as such defining where and how others harbor virus is imperative for eradication measures. To such ends, we used HIV-1_ADA-infected NOD.Cg-Prkdc ^scid Il2rg ^tm1Wjl /SzJ mice reconstituted with a human immune system to explore two long-acting ART regimens investigating their abilities to affect viral cell infection and latency. At 6 weeks of infection animals were divided into four groups. One received long-acting (LA) cabotegravir (CAB) and rilpivirine (RVP) (2ART), a second received LA CAB, lamivudine, abacavir and RVP (4ART), a third were left untreated and a fourth served as an uninfected control. After 4 weeks of LA ART treatment, blood, spleen and bone marrow (BM) cells were collected then phenotypically characterized. CD4+ T cell subsets, macrophages and hematopoietic progenitor cells were analyzed for HIV-1 nucleic acids by droplet digital PCR.

RESULTS

Plasma viral loads were reduced by two log₁₀ or to undetectable levels in the 2 and 4ART regimens, respectively. Numbers and distributions of CD4+ memory and regulatory T cells, macrophages and hematopoietic progenitor cells were significantly altered by HIV-1 infection and by both ART regimens. ART reduced viral DNA and RNA in all cell and tissue compartments. While memory cells were the dominant T cell reservoir, integrated HIV-1 DNA was also detected in the BM and spleen macrophages in both regimen-treated mice.

CONCLUSION

Despite vigorous ART regimens, HIV-1 DNA and RNA were easily detected in mature macrophages supporting their potential role as an infectious viral reservoir.

Dimethyl Fumarate Therapy Significantly Improves the Responsiveness of T Cells in Multiple Sclerosis Patients for Immunoregulation by Regulatory T Cells

Multiple sclerosis (MS) is a chronic autoimmune disease caused by an insufficient suppression of autoreactive T lymphocytes. One reason for the lack of immunological control is the reduced responsiveness of T effector cells (Teff) for the suppressive properties of regulatory T cells (Treg), a process termed Treg resistance. Here we investigated whether the disease-modifying therapy of relapsing-remitting MS (RRMS) with dimethyl fumarate (DMF) influences the sensitivity of T cells in the peripheral blood of patients towards Treg-mediated suppression. We demonstrated that DMF restores responsiveness of Teff to the suppressive function of Treg in vitro, presumably by down-regulation of interleukin-6R (IL-6R) expression on T cells. Transfer of human immune cells into immunodeficient mice resulted in a lethal graft-versus-host reaction triggered by human CD4⁺ Teff. This systemic inflammation can be prevented by activated Treg after transfer of immune cells from DMF-treated MS patients, but not after injection of Treg-resistant Teff from therapy-naïve MS patients. Furthermore, after DMF therapy, proliferation and expansion of T cells and the immigration into the spleen of the animals is reduced and modulated by activated Treg. In summary, our data reveals that DMF therapy significantly improves the responsiveness of Teff in MS patients to immunoregulation.

Changes in Frequency and Activation Status of Major CD4+ T-Cell Subsets after Initiation of Immunosuppressive Therapy in a Patient with New Diagnosis Childhood-Onset Systemic Lupus Erythematosus

BACKGROUND

Several studies suggest that defects of regulatory T-cells (Tregs) and impaired cellular immunity are secondary to an imbalance between auto-aggressive T-cells and Tregs in lupus patients. Discrepancies in Tregs and effector T-cells (Teff) in active lupus patients are shown to be restored in patients upon receiving immunosuppressive therapy. Therefore, our main aim was to observe frequencies of these CD4⁺ T-cell subsets and Tregs/Teff ratio in a new diagnosis of childhood-onset systemic lupus erythematous (cSLE) before and after initiation of therapy. In addition, we monitored T-cell exhaustion status by examining responses to super-antigen staphylococcal enterotoxin B (SEB) and PD-1 expression in this patient.

METHODS

Phenotyping of CD4⁺ T-cell subsets was carried out under basal conditions and after SEB stimulation using flow cytometry in one inactive (I-cSLE) and one active cSLE (A-cSLE) patient, as well as a healthy control (HC). The A-cSLE patient was a new diagnosis. Variables were measured at three consecutive time points in the active patient, reflecting various stages of disease activity. Activation status of CD4⁺ T-cells in the A-cSLE patient was compared to that of the I-cSLE patient and HC. Disease activity was measured by calculating the systemic lupus erythematous disease activity index.

RESULTS

We found that the A-cSLE patient was not Tregs deficient. The patient had increased frequency of Tregs, and the Tregs/Teff ratio increased when the disease activity became less severe. CD4⁺ T-cells in the I-cSLE patient and in the A-cSLE patient with milder disease activity had heightened responsiveness to SEB, whereas T-cells were relatively hypo-responsive to SEB in the A-cSLE patient when disease activity was higher. The active patient exhibited higher frequencies of PD-1⁺ expressing Tregs, Teff, and Tnaïve/mem cells under basal conditions compared to the HC and I-cSLE patient.

CONCLUSION

In the A-cSLE patient, changes in Tregs/Teff ratio correlated better with clinical improvement compared to Tregs frequencies alone and might reflect the restoration of immune homeostasis with therapy. SEB hypo-responsiveness in the A-cSLE patient when disease activity was higher paralleled with findings of greater frequencies of PD-1⁺ expressing Tregs, Teff, and Tnaïve/mem cells, suggests a possible global exhaustion status of CD4⁺ T-cells in this patient.

Pharmacodynamics of T cell function for monitoring pharmacologic immunosuppression after allogeneic hematopoietic stem cell transplantation

Information on pharmacodynamic monitoring after allogeneic hematopoietic cell transplantation (allo-SCT) to evaluate individual responses to immunosuppressive drugs is scarce. We studied the relationship between a panel of pharmacodynamic markers monitored during the first 3 months after transplant and the occurrence of graft-versus-host disease (GVHD). Lymphocyte activation assessed by intracellular ATP concentration in CD4⁺ T cells, a high percentage of CD8⁺ effector T cells, and a low percentage of CD4⁺ regulatory T (Treg) cells correlated significantly with GVHD. A cutoff value of 0.5 for the CD8⁺ effector T/Treg ratio provided the most accurate diagnosis of GVHD (sensitivity 58.8%, specificity 91%). These pharmacodynamic markers may provide an efficient complement to standard pharmacokinetic monitoring of immunosuppressive drugs after allo-SCT.

Novel molecular signatures in mononuclear cell populations from patients with systemic lupus erythematosus

To gain novel insights into the immunopathogenesis of systemic lupus erythematosus we have analyzed gene expression data from isolated CD4⁺ T cells, CD8⁺ T cells, CD19⁺ B cells, and CD56⁺ NK-cell enriched peripheral blood cell fractions from patients and healthy donors. As predicted, type I interferon-inducible gene transcripts are overexpressed in all populations. Transcripts preferentially expressed in SLE CD4⁺ and CD8⁺ T cells include those associated with Tregulatory and Th17 effector cell programs, respectively, but in each case additional transcripts predicted to limit differentiation of those effector cells are detected. Evidence for involvement of the Wnt/β-catenin pathway was observed in both B and T cell fractions, and novel transcripts were identified in each cell population. These data point to disrupted T effector cell differentiation and the Wnt/β-catenin pathway as contributors to immune dysfunction in SLE while further supporting a central role for the type I interferon pathway in lupus.

Retinoic acid-primed human dendritic cells inhibit Th9 cells and induce Th1/Th17 cell differentiation

All-trans-retinoic acid plays a central role in mucosal immunity, where it promotes its synthesis by up-regulating CD103 expression on dendritic cells, induces gut tropic (α4β7(+) and CCR9(+)) T cells, and inhibits Th1/Th17 differentiation. Recently, murine studies have highlighted the proinflammatory role of retinoic acid in maintaining inflammation under a variety of pathologic conditions. However, as a result of limited human data, we investigated the effect of retinoic acid on human dendritic cells and CD4(+) T cell responses in the presence of polarizing (Th1/Th9/Th17) and inflammatory (LPS-induced dendritic cells) conditions. We report a novel role of retinoic acid in an inflammatory setup, where retinoic acid-primed dendritic cells (retinoic acid-monocyte-derived dendritic cells) up-regulated CCR9(+)T cells, which were observed to express high levels of IFN-γ in the presence of Th1/Th17 conditions. Retinoic acid-monocyte-derived dendritic cells, under Th17 conditions, also favored the induction of IL-17(+) T cells. Furthermore, in the presence of TGF-β1 and IL-4, retinoic acid-monocyte-derived dendritic cells inhibited IL-9 and induced IFN-γ expression on T cells. Experiments with naïve CD4(+) T cells, activated in the presence of Th1/Th17 conditions and absence of DCs, indicated that retinoic acid inhibited IFN-γ and IL-17 expression on T cells. These data revealed that in the face of inflammatory conditions, retinoic acid, in contrast from its anti-inflammatory role, could maintain or aggravate the intestinal inflammation.

Effects of Malignant Melanoma Initiating Cells on T-Cell Activation

Although human malignant melanoma is a highly immunogenic cancer, both the endogenous antitumor immune response and melanoma immunotherapy often fail to control neoplastic progression. Accordingly, characterizing melanoma cell subsets capable of evading antitumor immunity could unravel optimized treatment strategies that might reduce morbidity and mortality from melanoma. By virtue of their preferential capacity to modulate antitumor immune responses and drive inexorable tumor growth and progression, malignant melanoma-initiating cells (MMICs) warrant closer investigation to further elucidate the cellular and molecular mechanisms underlying melanoma immune evasion and immunotherapy resistance. Here we describe methodologies that enable the characterization of immunoregulatory effects of purified MMICs versus melanoma bulk populations in coculture with syngeneic or allogeneic lymphocytes, using [3H]thymidine incorporation, enzyme-linked immunosorbent spot (ELISPOT), or ELISA assays. These assays were traditionally developed to analyze alloimmune processes and we successfully adapted them for the study of tumor-mediated immunomodulatory functions.

Interferon-Beta Therapy of Multiple Sclerosis Patients Improves the Responsiveness of T Cells for Immune Suppression by Regulatory T Cells

Multiple sclerosis (MS) is an inflammatory autoimmune disease characterized by imbalanced immune regulatory networks, and MS patient-derived T effector cells are inefficiently suppressed through regulatory T cells (Treg), a phenomenon known as Treg resistance. In the current study we investigated T cell function in MS patients before and after interferon-beta therapy. We compared cytokine profile, responsiveness for Treg-mediated suppression ex vivo and evaluated reactivity of T cells in vivo using a humanized mouse model. We found that CD4⁺ and CD8⁺ T cells of therapy-naive MS patients were resistant to Treg-mediated suppression. Treg resistance is associated with an augmented IL-6 production, enhanced IL-6 receptor expression, and increased PKB/c-Akt phosphorylation. These parameters as well as responsiveness of T cells to Treg-mediated suppression were restored after interferon-beta therapy of MS patients. Following transfer into immunodeficient mice, MS T cells induced a lethal graft versus host disease (GvHD) and in contrast to T cells of healthy volunteers, this aggressive T cell response could not be controlled by Treg, but was abolished by anti-IL-6 receptor antibodies. However, magnitude and lethality of GvHD induced by MS T cells was significantly decreased after interferon-beta therapy and the reaction was prevented by Treg activation in vivo. Our data reveals that interferon-beta therapy improves the immunoregulation of autoaggressive T effector cells in MS patients by changing the IL-6 signal transduction pathway, thus restoring their sensitivity to Treg-mediated suppression.

T-regulatory cells and programmed death 1+ T cells contribute to effector T-cell dysfunction in patients with chronic obstructive pulmonary disease

RATIONALE

Previous studies from our laboratory have shown that peripheral blood mononuclear cells (PBMCs) from patients with chronic obstructive pulmonary disease (COPD) prone to exacerbations with nontypeable Haemophilus influenzae have impaired responses to lipoprotein P6. We hypothesized that an underlying immunosuppressive network could be responsible for the defective antibacterial immunity observed in these patients. We evaluated T regulatory cells (Tregs), myeloid-derived suppressor cells (MDSC), and exhausted T effector cells (programmed death 1 [PD-1](+)) in patients with COPD, because these cells are known to play a pivotal role in suppressing immune responses.

OBJECTIVES

We performed an in-depth characterization of Tregs, T effector cells, and MDSC in COPD and correlated their levels and function with disease severity.

METHODS

Treg, effector T cell, and MDSC frequency from patients with COPD and healthy subjects' PBMCs were analyzed by flow cytometry. Treg immunosuppressive capacity was measured by in vitro suppression assay. The frequency of interferon-γ producing T cells and T-cell proliferation were measured after blocking CTLA-4 and PD-1. Plasma proinflammatory and immunosuppressive cytokine levels were measured.

MEASUREMENTS AND MAIN RESULTS

Significantly increased levels of Tregs, MDSC, and PD-1(+) exhausted effector T cells were present in patients with COPD compared with healthy subjects. Tregs from patients with COPD suppressed P6-specific T-cell proliferation to a greater extent than Tregs from healthy subjects. Plasma levels of Treg-generated cytokines, IL-10, and transforming growth factor-β were elevated. Blockade of CTLA-4 resulted in significant augmentation of T-cell IFN-γ production in patients with COPD.

CONCLUSIONS

Functionally suppressive Tregs, MDSCs, and exhausted PD-1(+) T cells contribute to effector T-cell dysfunction in COPD.

Modulation of Treg cells/T effector function by GITR signaling is context-dependent

Treg cells express high levels of the glucocorticoid-induced tumor necrosis factor-related receptor (GITR), while resting conventional T (Tconv) cells express low levels that are increased upon activation. Manipulation of GITR/GITR-Ligand (GITR-L) interactions results in enhancement of immune responses, but it remains unclear whether this enhancement is secondary to costimulation of Tconv cells or to reversal of Treg-cell-mediated suppression. Here, we used a nondepleting Fc-GITR-L and combinations of WT and GITR KO Treg cells and Tconv cells to reexamine the effects of GITR stimulation on each subpopulation in both unmanipulated mice and mice with inflammatory bowel disease. Treatment of mice with Fc-GITR-L resulted in significant expansion of Treg cells and a modest expansion of Tconv cells. When RAG KO mice were reconstituted with Tconv cells alone, GITR-L resulted in Tconv-cell expansion and severe inflammatory bowel disease. The protective effect of Treg cells was lost in the presence of Fc-GITR-L, secondary to death of the Treg cells. When RAG KO mice were reconstituted with Treg cells alone, the transferred cells expanded normally, and Fc-GITR-L treatment resulted in a loss of Foxp3 expression, but the ex-Treg cells did not cause any pathology. The effects of GITR activation are complex and depend on the host environment and the activation state of the Treg cells and T effector cells.

Intrahepatic IL-8 producing Foxp3⁺CD4⁺ regulatory T cells and fibrogenesis in chronic hepatitis C

BACKGROUND & AIMS

Regulatory CD4(+) T cells (Tregs) are considered to affect outcomes of HCV infection, because they increase in number during chronic hepatitis C and can suppress T-cell functions.

METHODS

Using microarray analysis, in situ immunofluorescence, ELISA, and flowcytometry, we characterised functional differentiation and localisation of adaptive Tregs in patients with chronic hepatitis C.

RESULTS

We found substantial upregulation of IL-8 in Foxp3(+)CD4(+) Tregs from chronic hepatitis C. Activated GARP-positive IL-8(+) Tregs were particularly enriched in livers of patients with chronic hepatitis C in close proximity to areas of fibrosis and their numbers were correlated with the stage of fibrosis. Moreover, Tregs induced upregulation of profibrogenic markers TIMP1, MMP2, TGF-beta1, alpha-SMA, collagen, and CCL2 in primary human hepatic stellate cells (HSC). HSC activation, but not Treg suppressor function, was blocked by adding a neutralizing IL-8 antibody.

CONCLUSIONS

Our studies identified Foxp3(+)CD4(+) Tregs as an additional intrahepatic source of IL-8 in chronic hepatitis C acting on HSC. Thus, Foxp3(+)CD4(+) Tregs in chronic hepatitis C have acquired differentiation as regulators of fibrogenesis in addition to suppressing local immune responses.