Functional plasticity in human FOXP3+regulatory T cells

Multiple infusions of ex vivo-expanded regulatory T cells promote CD163+ myeloid cells and kidney allograft survival in non-lymphodepleted non-human primates

Clinical verification of adoptively transferred regulatory T cell (Treg) efficacy in transplantation remains challenging. Here, we examined the influence of autologous ex vivo-expanded polyclonal Tregs on kidney graft survival in a clinically relevant non-human primate model. Peripheral blood Tregs were isolated and expanded using artificial antigen presenting cells. Immunosuppression was comprised of tapered tacrolimus and CTLA4 immunoglobulin, in five animals each without or with Treg infusions. Escalating Treg doses were administered 6, 10, 13, 16, 20, 23, 27 and 30 days after transplant. Infused Tregs were monitored for Treg signature, anti-apoptotic (Bcl-2) and proliferation (Ki67) marker expression. Treg infusions prolonged median graft survival time significantly from 35 to 70 days. Treg marker (Ki67 and Bcl-2) expression by infused Tregs diminished after their infusion but remained comparable to that of circulating native Tregs. No major changes in circulating donor-reactive T cell responses or total Treg percentages, or in graft-infiltrating T cell subsets were observed with Treg infusion. However, Treg infusion was associated with significant increases in CD163 expression by circulating HLA-DR+ myeloid cells and elevated levels of circulating soluble CD163. Further, graft-infiltrating CD163+ cells were increased with Treg infusion. Thus, multiple Treg infusions were associated with M2-like myeloid cell enhancement that may mediate immunomodulatory, anti-inflammatory and graft reparative effects.

Differential transcriptional and functional properties of regulatory T cells in HIV-infected individuals on antiretroviral therapy and long-term non-progressors

Objectives

Regulatory T cells (Tregs) are widely recognised as a subset of CD4⁺CD25⁺FOXP3⁺ T cells that have a key role in maintaining immune homeostasis. The impact of HIV‐1 infection on immunological properties and effector functions of Tregs has remained the topic of debate and controversy. In the present study, we investigated transcriptional profile and functional properties of Tregs in HIV‐1‐infected individuals either receiving antiretroviral therapy (ART, n = 50) or long‐term non‐progressors (LTNPs, n = 24) compared to healthy controls (HCs, n = 38).

Methods

RNA sequencing (RNAseq), flow cytometry‐based immunophenotyping and functional assays were performed to study Tregs in different HIV cohorts.

Results

Our RNAseq analysis revealed that Tregs exhibit different transcriptional profiles in HIV‐infected individuals. While Tregs from patients on ART upregulate pathways associated with a more suppressive (activated) phenotype, Tregs in LTNPs exhibit upregulation of pathways associated with impaired suppressive properties. These observations may explain a higher propensity for autoimmune diseases in LTNPs. Also, we found substantial upregulation of HLA‐F mRNA and HLA‐F protein in Tregs from HIV‐infected subjects compared to healthy individuals. These observations highlight a potential role for this non‐classical HLA in Tregs in the context of HIV infection, which should be investigated further in other chronic viral infections and cancer.

Conclusion

Our study has provided a novel insight into Tregs at the transcriptional and functional levels in different HIV‐infected groups.

Directed differentiation of regulatory T cells from naive T cells and prevention of their inflammation-mediated instability using small molecules

Regulatory T (T_reg ) cell therapy is a promising approach for immune tolerance induction in autoimmunity conditions and cell/organ transplantations. Insufficient isolation yields and impurity during downstream processes and T_reg instability after adoptive transfer in inflammatory conditions are major limitations to T_reg therapy, and indicate the importance of seeking a valid, reliable method for de-novo generation of T_regs . In this research, we evaluated T_reg -like cells obtained from different T_reg differentiation protocols in terms of their yield, purity and activity. Differentiation was performed on naive CD4⁺ cells and a naive CD4⁺ /T_reg co-culture by using three different protocols - ectopic expression of forkhead box protein P3 (E-FoxP3), soluble transforming growth factor β (S-TGF) and small molecules [N-acetyl puromycin and SR1555 (N-Ac/SR)]. The results showed that a high yield of a homogeneous population of T_reg -like cells could be achieved by the N-Ac/SR method under a T helper type 17 (Th17)-polarizing condition, particularly interleukin (IL)-6 and TGF-β, when compared with the E-FoxP3 and S-TGF methods. Surprisingly, SR completely inhibited the differentiation of IL-17-producing cells and facilitated T_reg generation in the inflammatory condition and had highly suppressive activity against T cell proliferation without T_reg -specific demethylase region (TSDR) demethylation. For the first time, to our knowledge, we report the generation of efficient, pure T_reg -like cells by using small molecules during in-vitro inflammatory conditions. Our results suggested that the N-Ac/SR method has several advantages for T_reg generation when compared with the other methods, including a higher purity of T_regs , easier procedure, superior suppressive activity during the inflammatory condition and decreased cost.

Adoptive Cell Therapy with Tregs to Improve Transplant Outcomes: The Promise and the Stumbling Blocks

The contribution of regulatory T cells (Treg) to the induction and maintenance of tolerance is well-recognized in rodents and may contribute to long-term human organ allograft survival. The therapeutic efficacy of adoptively-transferred Treg in promoting tolerance to organ allografts is well-recognized in mouse models. Early phase 1/2 clinical studies of Treg therapy have been conducted in patients with type-1 (autoimmune) diabetes and refractory Crohn's disease, and for inhibition of graft-versus-host disease following bone marrow transplantation with proven safety. The feasibility of adoptive Treg therapy in the clinic is subject to various parameters, including optimal cell source, isolation procedure, expansion, target dose, time of infusion, as well as generation of a GMP-cell product. Several phase 1/2 Treg dose-escalation studies are underway in organ transplantation. Recent evidence suggests that additional factors are critical to ensure Treg safety and efficacy in allograft recipients, including Treg characterization, stability, longevity, trafficking, concomitant immunosuppression, and donor antigen specificity. Accordingly, Treg therapy in the context of organ transplantation may prove more challenging in comparison to other prospective clinical settings of Treg immunotherapy, such as type-1 diabetes.

Hepatic stellate cells increase the immunosuppressive function of natural Foxp3+ regulatory T cells via IDO-induced AhR activation

Immunosuppressive, naturally occurring CD4⁺CD25⁺forkhead box p3⁺ (Foxp3⁺) regulatory T cells (nT_regs) offer potential for the treatment of immune-mediated inflammatory disorders. However, potential instability of ex vivo-expanded nT_regs following their adoptive transfer may be a significant limitation. LPS-stimulated hepatic stellate cells (HSCs) induce expansion and enhance the suppressive function and stability of allogeneic nT_regs We aimed to delineate mechanisms underlying HSC-induced expansion and increased potency of nT_regs HSCs and nT_regs were isolated from mouse livers and spleens, respectively. Following coculture with LPS-pretreated allogeneic HSCs (LPS/HSCs), proliferation of nT_regs was measured by CFSE dilution, and Foxp3 expression and acetylation were determined by immunoprecipitation (IP) and Western blotting analysis. Expression of various genes associated with immunologic tolerance was determined by quantitative RT-PCR (qRT-PCR). LPS stimulation increased the expression and activity of the immunoregulatory enzyme IDO1 in HSCs, and LPS/HSCs stimulated aryl hydrocarbon receptor (AhR) signaling in cocultured nT_regs Reciprocally, T_regs increased IDO1 expression in HSCs. IDO1^-/- LPS/HSCs were inferior to WT LPS/HSCs in stimulating nT_reg expansion. Pharmacologic inhibition of IDO1 in HSCs by 1-methyltryptophan (1MT) inhibited LPS/HSC-induced AhR signaling in nT_regs, which was responsible for their expansion, Foxp3 expression, and stabilization of Foxp3 by increasing acetylation of lysine residues. Finally, HSCs cryopreserved, following 2-3 passages, were as potent as primary-cultured HSCs in expanding nT_regs In conclusion, LPS/HSCs expand allogeneic nT_regs through an IDO-dependent, AhR-mediated mechanism and increase their stability through lysine-acetylation of Foxp3. nT_regs expanded by cryopreserved HSCs may have potential for clinical use.

Regulatory T Cell Infusion Can Enhance Memory T Cell and Alloantibody Responses in Lymphodepleted Nonhuman Primate Heart Allograft Recipients

The ability of regulatory T cells (Treg) to prolong allograft survival and promote transplant tolerance in lymphodepleted rodents is well established. Few studies, however, have addressed the therapeutic potential of adoptively transferred, CD4(+) CD25(+) CD127(-) Foxp3(+) (Treg) in clinically relevant large animal models. We infused ex vivo-expanded, functionally stable, nonselected Treg (up to a maximum cumulative dose of 1.87 billion cells) into antithymocyte globulin-lymphodepleted, MHC-mismatched cynomolgus monkey heart graft recipients before homeostatic recovery of effector T cells. The monkeys also received tacrolimus, anti-interleukin-6 receptor monoclonal antibodies and tapered rapamycin maintenance therapy. Treg administration in single or multiple doses during the early postsurgical period (up to 1 month posttransplantation), when host T cells were profoundly depleted, resulted in inferior graft function compared with controls. This was accompanied by increased incidences of effector memory T cells, enhanced interferon-γ production by host CD8(+) T cells, elevated levels of proinflammatory cytokines, and antidonor alloantibodies. The findings caution against infusion of Treg during the early posttransplantation period after lymphodepletion. Despite marked but transient increases in Treg relative to endogenous effector T cells and use of reputed "Treg-friendly" agents, the host environment/immune effector mechanisms instigated under these conditions can perturb rather than favor the potential therapeutic efficacy of adoptively transferred Treg.

Biased Treg/Th17 balance away from regulatory toward inflammatory phenotype in relapsed multiple sclerosis and its correlation with severity of symptoms

The opposing immune functions of Treg and Th17 lymphocytes and the plasticity of Treg/Th17 differentiation, has led us to investigate the effects of their fluctuations and counterbalance in autoimmune condition of multiple sclerosis (MS). Evaluation of Treg and Th17 frequency in peripheral blood of a group of relapsed MS patients, showed a decrease in Treg/Th17 ratio compared to that of healthy controls. A reverse correlation between these subsets was observed in controls but not in patient groups. Both Treg frequency and Treg/Th17 ratio were negatively correlated with severity of symptoms. There was shown to be an enduring increase in Treg frequency associated with MS disease.

Autologous regulatory T cells for the treatment of type 1 diabetes

The immune system is tasked with defending the host from a wide array of pathogens and environmental insults. When uncontrolled, this endeavor may lead to off-target reactivity to self-tissues resulting in multiple autoimmune diseases including type 1 diabetes (T1D). This multifactorial disease process involves over 40 susceptibility genes and is influenced by poorly characterized environmental factors. While many questions regarding the pathogenesis of the disease process remain, it has become increasingly clear that the progression to disease results from a breakdown in the processes that maintain peripheral immune tolerance. The end result of this process is localized tissue inflammation, islet dysfunction, and ultimately the destruction of pancreatic β cells due to concomitant defects in innate and adaptive immune responses. A number of immunomodulatory intervention trials have now been conducted in patients at risk for or with recent onset T1D, often with the goal of restoring immune tolerance by inducing regulatory T cells (Tregs). Unfortunately, many of these trials have fallen short of inducing persistent immune regulation. This shortfall has led to additional efforts to more directly shift the balance from destructive effector T cell (Teff) responses to favor Tregs, including the use of autologous Treg cell therapy. In this review we will discuss key concepts related to the use of autologous Treg cell therapy for the treatment of T1D. Among these topics, we will discuss the notions of genetic control of Treg activity, Treg cellular plasticity, and requirements for antigen-specificity.

Functional stability of Foxp3+ regulatory T cells

Significant evidence demonstrates that CD4(+) regulatory T cells (T(reg)) expressing the Forkhead box P3 (Foxp3) transcription factor are a distinct lineage of CD4(+) T cells that are essential for maintaining self-tolerance and modulating immunity to various nonself-antigens under changing inflammatory settings. Stable Foxp3 expression ensures T(reg) function in a variety of inflammatory contexts. However, the model of T(reg) cells as a stable, long-lived lineage is controversial. Whereas some studies have observed long-lived T(reg) function, recent studies suggest that T(reg) cells adapt to microenvironmental changes and consequently manifest functional plasticity by reprogramming into inflammatory T cells. Here, we review the evidence addressing the functional stability or plasticity of Foxp3(+) T(reg) cells and the implications for immune homeostasis and disease.