Inhibition of activation induced CD154 on CD4 + CD25 − cells: a valid surrogate for human Treg suppressor function

The Role of Regulatory T Cells and Their Therapeutic Potential in Hypertensive Disease of Pregnancy: A Literature Review

Hypertensive disorders of pregnancy (HDP), including preeclampsia (PE) and gestational hypertension (GH), are major causes of maternal and foetal morbidity and mortality. This review elucidates the role of regulatory T cells (Tregs) in the immunological aspects of HDP and explores their therapeutic potential. Tregs, which play a critical role in maintaining immune homeostasis, are crucial in pregnancy to prevent immune-mediated rejection of the foetus. The review highlights that Tregs contribute to immunological adaptation in normal pregnancy, ensuring foetal acceptance. In contrast, HDP is associated with Treg dysfunction, which is marked by decreased numbers and impaired regulatory capacity, leading to inadequate immune tolerance and abnormal placental development. This dysfunction is particularly evident in PE, in which Tregs fail to adequately modulate the maternal immune response against foetal antigens, contributing to the pathophysiology of the disorder. Therapeutic interventions aiming to modulate Treg activity represent a promising avenue for HDP management. Studies in animal models and limited clinical trials suggest that enhancing Treg functionality could mitigate HDP symptoms and improve pregnancy outcomes. However, given the multifactorial nature of HDP and the intricate regulatory mechanisms of Tregs, the review explores the complexities of translating in vitro and animal model findings into effective clinical therapies. In conclusion, while the precise role of Tregs in HDP is still being unravelled, their central role in immune regulation during pregnancy is indisputable. Further research is needed to fully understand the mechanisms by which Tregs contribute to HDP and to develop targeted therapies that can safely and effectively harness their regulatory potential for treating hypertensive diseases of pregnancy.

Searching for Peptide Inhibitors of T Regulatory Cell Activity by Targeting Specific Domains of FOXP3 Transcription Factor

(1) Background: The ability of cancer cells to evade the immune system is due in part to their capacity to induce and recruit T regulatory cells (Tregs) to the tumor microenvironment. Strategies proposed to improve antitumor immunity by depleting Tregs generally lack specificity and raise the possibility of autoimmunity. Therefore, we propose to control Tregs by their functional inactivation rather than depletion. Tregs are characterized by the expression of the Forkhead box protein 3 (FOXP3) transcription factor, which is considered their “master regulator”. Its interaction with DNA is assisted primarily by its interaction with other proteins in the so-called “Foxp3 interactome”, which elicits much of the characteristic Treg cell transcriptional signature. We speculated that the disruption of such a protein complex by using synthetic peptides able to bind Foxp3 might have an impact on the functionality of Treg cells and thus have a therapeutic potential in cancer treatment. (2) Methods: By using a phage-displayed peptide library, or short synthetic peptides encompassing Foxp3 fragments, or by studying the crystal structure of the Foxp3:NFAT complex, we have identified a series of peptides that are able to bind Foxp3 and inhibit Treg activity. (3) Results: We identified some peptides encompassing fragments of the leuzin zipper or the C terminal domain of Foxp3 with the capacity to inhibit Treg activity in vitro. The acetylation/amidation of linear peptides, head-to-tail cyclization, the incorporation of non-natural aminoacids, or the incorporation of cell-penetrating peptide motifs increased in some cases the Foxp3 binding capacity and Treg inhibitory activity of the identified peptides. Some of them have shown antitumoral activity in vivo. (4) Conclusions: Synthetic peptides constitute an alternative to inhibit Foxp3 protein–protein interactions intracellularly and impair Treg immunosuppressive activity. These peptides might be considered as potential hit compounds on the design of new immunotherapeutic approaches against cancer.

Operational tolerance in intestinal transplantation

By presenting the first case report of true operational tolerance in an intestinal transplant patient, we aim to demonstrate that tolerance is possible in a field that has been hampered by suboptimal outcomes. Although operational tolerance has been achieved in liver and kidney transplantation, and some intestinal transplant patients have been able to decrease immunosuppression, this is the first instance of true operational tolerance after complete cessation of immunosuppression. A patient received a deceased-donor small intestinal and colon allograft with standard immunosuppressive treatment, achieving excellent graft function after overcoming a graft-versus-host-disease episode 5 months posttransplant. Four years later, against medical advice, the patient discontinued all immunosuppression. During follow-up visits 2 and 3 years after cessation of immunosuppression, the patient exhibited normal graft function with full enteral autonomy and without histological or endoscopic signs of rejection. Mechanistic analysis demonstrated immune competence against third party antigen, with in vitro evidence of donor-specific hyporesponsiveness in the absence of donor macrochimerism. This proof of principle case can stimulate future mechanistic studies on diagnostic and therapeutic strategies, for example, cellular therapy trials, that can lead to minimization or elimination of immunosuppression and, it is hoped, help revitalize the field of intestinal transplantation.

Dawn of Monitoring Regulatory T Cells in (Pre-)clinical Studies: Their Relevance Is Slowly Recognised

Regulatory T cells (Tregs) have a prominent role in the control of immune homeostasis. Pharmacological impact on their activity or balance with effector T cells could contribute to (impaired) clinical responses or adverse events. Monitoring treatment-related effects on T cell subsets may therefore be part of (pre-)clinical studies for medicinal products. However, the extent of immune monitoring performed in studies for marketing authorisation and the degree of correspondence with data available in the public domain is not known. We evaluated the presence of T cell immunomonitoring in 46 registration dossiers of monoclonal antibodies indicated for immune-related disorders and published scientific papers. We found that the depth of Treg analysis in registration dossiers was rather small. Nevertheless, data on treatment-related Treg effects are available in public academia-driven studies (post-registration) and suggest that Tregs may act as a biomarker for clinical responses. However, public data are fragmented and obtained with heterogeneity of experimental approaches from a diversity of species and tissues. To reveal the potential added value of T cell (and particular Treg) evaluation in (pre-)clinical studies, more cell-specific data should be acquired, at least for medicinal products with an immunomodulatory mechanism. Therefore, extensive analysis of T cell subset contribution to clinical responses and the relevance of treatment-induced changes in their levels is needed. Preferably, industry and academia should work together to obtain these data in a standardised manner and to enrich our knowledge about T cell activity in disease pathogenesis and therapies. This will ultimately elucidate the necessity of T cell subset monitoring in the therapeutic benefit-risk assessment.

Therapeutic Potential of Regulatory T Cells in Preeclampsia-Opportunities and Challenges

Inflammation is a central feature and is implicated as a causal factor in preeclampsia and other hypertensive disorders of pregnancy. Inflammatory mediators and leukocytes, which are elevated in peripheral blood and gestational tissues, contribute to the uterine vascular anomalies and compromised placental function that characterize particularly the severe, early onset form of disease. Regulatory T (Treg) cells are central mediators of pregnancy tolerance and direct other immune cells to counteract inflammation and promote robust placentation. Treg cells are commonly perturbed in preeclampsia, and there is evidence Treg cell insufficiency predates onset of symptoms. A causal role is implied by mouse studies showing sufficient numbers of functionally competent Treg cells must be present in the uterus from conception, to support maternal vascular adaptation and prevent later placental inflammatory pathology. Treg cells may therefore provide a tractable target for both preventative strategies and treatment interventions in preeclampsia. Steps to boost Treg cell activity require investigation and could be incorporated into pregnancy planning and preconception care. Pharmacological interventions developed to target Treg cells in autoimmune conditions warrant consideration for evaluation, utilizing rigorous clinical trial methodology, and ensuring safety is paramount. Emerging cell therapy tools involving in vitro Treg cell generation and/or expansion may in time become relevant. The success of preventative and therapeutic approaches will depend on resolving several challenges including developing informative diagnostic tests for Treg cell activity applicable before conception or during early pregnancy, selection of relevant patient subgroups, and identification of appropriate windows of gestation for intervention.

Regulatory perspective on in vitro potency assays for human mesenchymal stromal cells used in immunotherapy

Mesenchymal stromal cells (MSCs) are multipotent cells derived from various tissues that can differentiate into several cell types. MSCs are able to modulate the response of immune cells of the innate and adaptive immune system. Because of these multimodal properties, the potential use of MSCs for immunotherapies is currently explored in various clinical indications. Due to the diversity of potential MSC medicinal products at the level of cell source, manufacturing process and indication, distinct functionality tests may be needed to ensure the quality for each of the different products. In this review, we focus on in vitro potency assays proposed for characterization and release of different MSC medicinal products. We discuss the most used functional assays, as presented in scientific advices and literature, highlighting specific advantages and limitations of the various assays. Currently, the most proposed and accepted potency assay for release is based on in vitro inhibition of T cell proliferation or other functionalities. However, for some products, assays based on other MSC or responder cell properties may be more appropriate. In all cases, the biological relevance of the proposed assay for the intended clinical activity should be substantiated with appropriate product-specific (non-)clinical data. In case practical considerations prevent the use of the ideal potency assay at release, use of a surrogate marker or test could be considered if correlation with functionality has been demonstrated. Nevertheless, as the field of MSC immunology is evolving, improvements can be expected in relevant assays and consequently in guidance related to potency testing.

A novel method for assaying human regulatory T cell direct suppression of B cell effector function

We have established a highly reproducible and reliable protocol for testing human regulatory T cell function in suppressing IgM production from an immature human B cell line. The autoreactive Ramos B cell line provides a stable reporter of B cell effector function that can be tested by a straight-forward IgM ELISA. Tregs from healthy volunteers display a range of ability for suppressing baseline IgM production in a contact- and death-independent manner. Having established the normal range for human Treg direct suppression of B cell effector function, it will now be possible to efficiently test Tregs from various autoimmune conditions in which B cell hyperactivity and secretion of auto-antibodies are a hallmark of disease.

Reduced Numbers and Impaired Function of Regulatory T Cells in Peripheral Blood of Ischemic Stroke Patients

Background and Purpose. Regulatory T cells (Tregs) have been suggested to modulate stroke-induced immune responses. However, analyses of Tregs in patients and in experimental stroke have yielded contradictory findings. We performed the current study to assess the regulation and function of Tregs in peripheral blood of stroke patients. Age dependent expression of CD39 on Tregs was quantified in mice and men. Methods. Total FoxP3⁺ Tregs and CD39⁺FoxP3⁺ Tregs were quantified by flow cytometry in controls and stroke patients on admission and on days 1, 3, 5, and 7 thereafter. Treg function was assessed by quantifying the inhibition of activation-induced expression of CD69 and CD154 on T effector cells (Teffs). Results. Total Tregs accounted for 5.0% of CD4⁺ T cells in controls and <2.8% in stroke patients on admission. They remained below control values until day 7. CD39⁺ Tregs were most strongly reduced in stroke patients. On day 3 the Treg-mediated inhibition of CD154 upregulation on CD4⁺ Teff was impaired in stroke patients. CD39 expression on Treg increased with age in peripheral blood of mice and men. Conclusion. We demonstrate a loss of active FoxP3⁺CD39⁺ Tregs from stroke patient's peripheral blood. The suppressive Treg function of remaining Tregs is impaired after stroke.

Interleukin-17A-Induced Human Mesenchymal Stem Cells Are Superior Modulators of Immunological Function

Interferon-γ (IFN-γ)-preactivated mesenchymal stem cells (MSC-γ) are highly immunosuppressive but immunogenic in vivo due to their inherent expression of major histocompatibility (MHC) molecules. Here, we present an improved approach where we modified human bone marrow-derived MSC with interleukin-17A (MSC-17) to enhance T cell immunosuppression but not their immunogenicity. MSC-17, unlike MSC-γ, showed no induction or upregulation of MHC class I, MHC class II, and T cell costimulatory molecule CD40, but maintained normal MSC morphology and phenotypic marker expression. When cocultured with phytohemagglutinin (PHA)-activated human T cells, MSCs-17 were potent suppressors of T cell proliferation. Furthermore, MSC-17 inhibited surface CD25 expression and suppressed the elaboration of Th1 cytokines, IFN-γ, tumor necrosis factor-α (TNF-α), and IL-2 when compared with untreated MSCs (UT-MSCs). T cell suppression by MSC-17 correlated with increased IL-6 but not with indoleamine 2,3-dioxygenase 1, cyclooxygenase 1, and transforming growth factor β-1. MSC-17 but not MSC-γ consistently induced CD4(+) CD25(high) CD127(low) FoxP3(+) regulatory T cells (iTregs) from PHA-activated CD4(+) CD25(-) T cells. MSC-induced iTregs expressed CD39, CD73, CD69, OX40, cytotoxic T-lymphocyte associated antigen-4 (CTLA-4), and glucocorticoid-induced TNFR-related protein (GITR). These suppressive MSCs-17 can engender Tregs to potently suppress T cell activation with minimal immunogenicity and thus represent a superior T cell immunomodulator for clinical application.