Adoptive regulatory T cell therapy: challenges in clinical transplantation:

Cytolytic CD4+ and CD8+ Regulatory T-Cells and Implications for Developing Immunotherapies to Combat Graft-Versus-Host Disease

Regulatory T-cells (Treg) are critical for the maintenance of immune homeostasis and tolerance induction. While the immunosuppressive mechanisms of Treg have been extensively investigated for decades, the mechanisms responsible for Treg cytotoxicity and their therapeutic potential in regulating immune responses have been incompletely explored and exploited. Conventional cytotoxic T effector cells (Teffs) are known to be important for adaptive immune responses, particularly in the settings of viral infections and cancer. CD4+ and CD8+ Treg subsets may also share similar cytotoxic properties with conventional Teffs. Cytotoxic effector Treg (cyTreg) are a heterogeneous population in the periphery that retain the capacity to suppress T-cell proliferation and activation, induce cellular apoptosis, and migrate to tissues to ensure immune homeostasis. The latter can occur through several cytolytic mechanisms, including the Granzyme/Perforin and Fas/FasL signaling pathways. This review focuses on the current knowledge and recent advances in our understanding of cyTreg and their potential application in the treatment of human disease, particularly Graft-versus-Host Disease (GVHD).

Immunosuppressive PLGA TGF-β1 Microparticles Induce Polyclonal and Antigen-Specific Regulatory T Cells for Local Immunomodulation of Allogeneic Islet Transplants

Allogeneic islet transplantation is a promising cell-based therapy for Type 1 Diabetes (T1D). The long-term efficacy of this approach, however, is impaired by allorejection. Current clinical practice relies on long-term systemic immunosuppression, leading to severe adverse events. To avoid these detrimental effects, poly(lactic-co-glycolic acid) (PLGA) microparticles (MPs) were engineered for the localized and controlled release of immunomodulatory TGF-β1. The in vitro co-incubation of TGF-β1 releasing PLGA MPs with naïve CD4⁺ T cells resulted in the efficient generation of both polyclonal and antigen-specific induced regulatory T cells (iTregs) with robust immunosuppressive function. The co-transplantation of TGF-β1 releasing PLGA MPs and Balb/c mouse islets within the extrahepatic epididymal fat pad (EFP) of diabetic C57BL/6J mice resulted in the prompt engraftment of the allogenic implants, supporting the compatibility of PLGA MPs and local TGF-β1 release. The presence of the TGF-β1-PLGA MPs, however, did not confer significant graft protection when compared to untreated controls, despite measurement of preserved insulin expression, reduced intra-islet CD3⁺ cells invasion, and elevated CD3⁺Foxp3⁺ T cells at the peri-transplantation site in long-term functioning grafts. Examination of the broader impacts of TGF-β1/PLGA MPs on the host immune system implicated a localized nature of the immunomodulation with no observed systemic impacts. In summary, this approach establishes the feasibility of a local and modular microparticle delivery system for the immunomodulation of an extrahepatic implant site. This approach can be easily adapted to deliver larger doses or other agents, as well as multi-drug approaches, within the local graft microenvironment to prevent transplant rejection.

Gut Microbiota and Liver Interaction through Immune System Cross-Talk: A Comprehensive Review at the Time of the SARS-CoV-2 Pandemic

Background and aims: The gut microbiota is a complex ecosystem containing bacteria, viruses, fungi, yeasts and other single-celled organisms. It is involved in the development and maintenance of both innate and systemic immunity of the body. Emerging evidence has shown its role in liver diseases through the immune system cross-talk. We review herein literature data regarding the triangular interaction between gut microbiota, immune system and liver in health and disease. Methods: We conducted a search on the main medical databases for original articles, reviews, meta-analyses, randomized clinical trials and case series using the following keywords and acronyms and their associations: gut microbiota, microbiome, gut virome, immunity, gastrointestinal-associated lymphoid tissue (GALT), non-alcoholic fatty liver disease (NAFLD), non-alcoholic steato-hepatitis (NASH), alcoholic liver disease, liver cirrhosis, hepatocellular carcinoma. Results: The gut microbiota consists of microorganisms that educate our systemic immunity through GALT and non-GALT interactions. The latter maintain health but are also involved in the pathophysiology and in the outcome of several liver diseases, particularly those with metabolic, toxic or immune-mediated etiology. In this context, gut virome has an emerging role in liver diseases and needs to be further investigated, especially due to the link reported between severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection and hepatic dysfunctions. Conclusions: Changes in gut microbiota composition and alterations in the immune system response are involved in the pathogenesis of metabolic and immune-mediated liver diseases.

In situ recruitment of regulatory T cells promotes donor-specific tolerance in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) encompasses face and limb transplantation, but as with organ transplantation, it requires lifelong regimens of immunosuppressive drugs to prevent rejection. To achieve donor-specific immune tolerance and reduce the need for systemic immunosuppression, we developed a synthetic drug delivery system that mimics a strategy our bodies naturally use to recruit regulatory T cells (T_reg) to suppress inflammation. Specifically, a microparticle-based system engineered to release the T_reg-recruiting chemokine CCL22 was used in a rodent hindlimb VCA model. These "Recruitment-MP" prolonged hindlimb allograft survival indefinitely (>200 days) and promoted donor-specific tolerance. Recruitment-MP treatment enriched T_reg populations in allograft skin and draining lymph nodes and enhanced T_reg function without affecting the proliferative capacity of conventional T cells. With implications for clinical translation, synthetic human CCL22 induced preferential migration of human T_reg in vitro. Collectively, these results suggest that Recruitment-MP promote donor-specific immune tolerance via local enrichment of suppressive T_reg.

Treg-inducing microparticles promote donor-specific tolerance in experimental vascularized composite allotransplantation

For individuals who sustain devastating composite tissue loss, vascularized composite allotransplantation (VCA; e.g., hand and face transplantation) has the potential to restore appearance and function of the damaged tissues. As with solid organ transplantation, however, rejection must be controlled by multidrug systemic immunosuppression with substantial side effects. As an alternative therapeutic approach inspired by natural mechanisms the body uses to control inflammation, we developed a system to enrich regulatory T cells (Tregs) in an allograft. Microparticles were engineered to sustainably release TGF-β1, IL-2, and rapamycin, to induce Treg differentiation from naïve T cells. In a rat hindlimb VCA model, local administration of this Treg-inducing system, referred to as TRI-MP, prolonged allograft survival indefinitely without long-term systemic immunosuppression. TRI-MP treatment reduced expression of inflammatory mediators and enhanced expression of Treg-associated cytokines in allograft tissue. TRI-MP also enriched Treg and reduced inflammatory Th1 populations in allograft draining lymph nodes. This local immunotherapy imparted systemic donor-specific tolerance in otherwise immunocompetent rats, as evidenced by acceptance of secondary skin grafts from the hindlimb donor strain and rejection of skin grafts from a third-party donor strain. Ultimately, this therapeutic approach may reduce, or even eliminate, the need for systemic immunosuppression in VCA or solid organ transplantation.

Chimeric antigen receptor-engineered regulatory T lymphocytes: promise for immunotherapy of autoimmune disease

Regulatory T lymphocytes (Tregs) exist as natural ideal immunosuppressors in the immune system. Autologous or allogeneic Treg transfusion therapy has been carried out in animal models and humans as a new strategy for treating autoimmune disease. Recent studies have shown that Tregs can be engineered with chimeric antigen receptors to be antigen-specific, which are more effective than polyclonal Tregs with fewer target limitations and a lack of major histocompatibility complex restriction. This review describes the potential for applying chimeric antigen receptor-engineered regulatory T cells in autoimmune diseases.

Ex vivo expanded natural regulatory T cells from patients with end-stage renal disease or kidney transplantation are useful for autologous cell therapy

Novel concepts employing autologous, ex vivo expanded natural regulatory T cells (nTreg) for adoptive transfer has potential to prevent organ rejection after kidney transplantation. However, the impact of dialysis and maintenance immunosuppression on the nTreg phenotype and peripheral survival is not well understood, but essential when assessing patient eligibility. The current study investigates regulatory T-cells in dialysis and kidney transplanted patients and the feasibility of generating a clinically useful nTreg product from these patients. Heparinized blood from 200 individuals including healthy controls, dialysis patients with end stage renal disease and patients 1, 5, 10, 15, 20 years after kidney transplantation were analyzed. Differentiation and maturation of nTregs were studied by flow cytometry in order to compare dialysis patients and kidney transplanted patients under maintenance immunosuppression to healthy controls. CD127 expressing CD4⁺CD25^highFoxP3⁺ nTregs were detectable at increased frequencies in dialysis patients with no negative impact on the nTreg end product quality and therapeutic usefulness of the ex vivo expanded nTregs. Further, despite that immunosuppression mildly altered nTreg maturation, neither dialysis nor pharmacological immunosuppression or previous acute rejection episodes impeded nTreg survival in vivo. Accordingly, the generation of autologous, highly pure nTreg products is feasible and qualifies patients awaiting or having received allogenic kidney transplantation for adoptive nTreg therapy. Thus, our novel treatment approach may enable us to reduce the incidence of organ rejection and reduce the need of long-term immunosuppression.

Gene editing for inflammatory disorders

Technology for precise and efficient genetic editing is constantly evolving and is now capable of human clinical applications. Autoimmune and inflammatory diseases are chronic, disabling, sometimes life-threatening, conditions that feature heritable components. Both primary genetic lesions and the inflammatory pathobiology underlying these diseases represent fertile soil for new therapies based on the capabilities of gene editing. The ability to orchestrate precise targeted modifications to the genome will likely enable cell-based therapies for inflammatory diseases such as monogenic autoinflammatory disease, acquired autoimmune disease and for regenerative medicine in the setting of an inflammatory environment. Here, we discuss recent advances in genome editing and their evolving applications in immunoinflammatory diseases. Strengths and limitations of older genetic modification tools are compared with CRISPR/Cas9, base editing, RNA editing, targeted activators and repressors of transcription and targeted epigenetic modifiers. Commonly employed delivery vehicles to target cells or tissues of interest with genetic modification machinery, including viral, non-viral and cellular vectors, are described. Finally, applications in animal and human models of inflammatory diseases are discussed. Use of chimeric autoantigen receptor T cells, correction of monogenic diseases with genetically edited haematopoietic stem and progenitor cells, engineering of induced pluripotent stem cells and ex vivo expansion and modification of regulatory T cells for a range of chronic inflammatory diseases are reviewed.

Gene Therapy-Induced Antigen-Specific Tregs Inhibit Neuro-inflammation and Reverse Disease in a Mouse Model of Multiple Sclerosis

The devastating neurodegenerative disease multiple sclerosis (MS) could substantially benefit from an adeno-associated virus (AAV) immunotherapy designed to restore a robust and durable antigen-specific tolerance. However, developing a sufficiently potent and lasting immune-regulatory therapy that can intervene in ongoing disease is a major challenge and has thus been elusive. We addressed this problem by developing a highly effective and robust tolerance-inducing in vivo gene therapy. Using a pre-clinical animal model, we designed a liver-targeting gene transfer vector that expresses full-length myelin oligodendrocyte glycoprotein (MOG) in hepatocytes. We show that by harnessing the tolerogenic nature of the liver, this powerful gene immunotherapy restores immune tolerance by inducing functional MOG-specific regulatory T cells (Tregs) in vivo, independent of major histocompatibility complex (MHC) restrictions. We demonstrate that mice treated prophylactically are protected from developing disease and neurological deficits. More importantly, we demonstrate that when given to mice with preexisting disease, ranging from mild neurological deficits to severe paralysis, the gene immunotherapy abrogated CNS inflammation and significantly reversed clinical symptoms of disease. This specialized approach for inducing antigen-specific immune tolerance has significant therapeutic potential for treating MS and other autoimmune disorders.

Low utility of serum 25-hydroxyvitamin D3 and 1, 25-dihydroxyvitamin D3 in predicting peripheral Treg and Th17 cell counts in ESRD and renal transplant patients

BACKGROUND

Vitamin D has shown an immune-modulatory effect in different studies. Vitamin D stimulates Tregs and inhibits Th17 cells. The immune-modulatory role of vitamin D in chronic kidney disease (CKD) and renal transplant patients is unclear. We measured whether different serum levels of vitamin D were associated with an increased or decreased presence of lymphocyte subsets including Treg and Th17 cells in end-stage renal disease (ESRD) and renal transplant recipients.

METHODS

Eighty-seven renal transplant recipients and 53 end-stage renal disease (ESRD) patients were enrolled in this study. The absolute counts of CD4+ and CD8+ T, CD16+ CD56+ NK, CD19+ B, CD4+ CD25+ CD127- Foxp3+ (Tregs), Helios+ Tregs, CD38+ Tregs, and CD4+ CD17+ (Th17) cells were analyzed in peripheral blood in both patient groups. In addition, serum 25 (OH) D₃, 1, 25 (OH)₂ D₃, IL-6, IL-17, IL-23, and TGF-β₁ were measured. The association between lymphocyte subset counts and 1, 25 (OH)₂ D₃ or 25 (OH) D₃ was studied, as was the association between serum IL-6, IL-17, IL-23, or TGF-β₁ and 1,25 (OH)₂ D₃ or 25 (OH) D₃.

RESULTS

Serum 25 (OH) D₃ and 1,25 (OH)₂ D₃ levels were not independently associated with peripheral CD4+ T, CD19+ B, CD16+ CD56+ NK, Treg, or Th17 cell counts. In contrast to serum 25 (OH) D₃, serum1, 25 (OH)₂ D₃ was positively associated with CD8+ T cells counts in renal transplant recipients.

CONCLUSION

Our findings indicate low utility of serum 25 (OH) D₃ and 1, 25 (OH)₂ D₃ levels in predicting a change in lymphocyte subset counts in ESRD and renal transplant patients.

Abnormal phenotypic distribution of regulatory and effector T cells in octogenarian and nonagenarian women

INTRODUCTION

aging is associated with several immunologic changes. Regulatory (Treg) and effector T cells are involved in the pathogenesis of infectious, neoplastic, and autoimmune diseases. Little is known about the effects of aging on the frequency and function of these T cell subpopulations.

METHODS

peripheral blood mononuclear cells (PBMC) were obtained from 26 young (under 44 years old) and 18 elderly (above 80 years old) healthy women. T cell subpopulations were analyzed by flow cytometry.

RESULTS

elderly individuals had lower frequency of several activated effector T cell phenotypes as compared with young individuals: CD3+CD4+CD25+ (3.82±1.93 versus 9.53±4.49; p<0.0001); CD3+CD4+CD25+CD127+(2.39±1.19 versus 7.26±3.84; p<0.0001); CD3+CD4+CD25+ (0.41±0.22 versus 1.86±0.85, p<0.0001); and CD3+CD4+CD25highCD127+(0.06±0.038 versus 0.94±0.64, p<0.0001). Treg (CD3+CD4+CD25+CD127øFoxp3+) presented lower frequency in elderly individuals as compared to young adults (0.34±0.18 versus 0.76±0.48; p=0.0004) and its frequency was inversely correlated with age in the whole group (r=-0.439; p=0.013). The elderly group showed higher frequency of two undefined CD25øFoxp3+ phenotypes: CD3+CD4+CD25øFoxp3+(15.05±7.34 versus 1.65±1.71; p<0.0001) and CD3+CD4+CD25øCD127øFoxp3+(13.0±5.52 versus 3.51±2.87; p<0.0001).

CONCLUSIONS

the altered proportion of different T cell subsets herein documented in healthy elderly women may be relevant to the understanding of the immunologic behavior and disease susceptibility patterns observed in geriatric patients.

Regulatory T Cells and Their Role in Animal Disease

In humans and mouse models, Foxp3(+) regulatory T cells are known to control all aspects of immune responses. However, only limited information exists on these cells' role in diseases of other animals. In this review, we cover the most important features and different types of regulatory T cells, which include those that are thymus-derived and peripherally induced, the mechanisms by which they control immune responses by targeting effector T cells and antigen-presenting cells, and most important, their role in animal health and diseases including cancer, infections, and other conditions such as hypersensitivities and autoimmunity. Although the literature regarding regulatory T cells in domestic animal species is still limited, multiple articles have recently emerged and are discussed. Moreover, we also discuss the evidence suggesting that regulatory T cells might limit the magnitude of effector responses, which can have either a positive or negative result, depending on the context of animal and human disease. In addition, the issue of plasticity is discussed because plasticity in regulatory T cells can result in the loss of their protective function in some microenvironments during disease. Lastly, the manipulation of regulatory T cells is discussed in assessing the possibility of their use as a treatment in the future.

Microbiota, immunity and the liver

The gut harbors a complex community of over 100 trillion microbial cells known to exist in symbiotic harmony with the host influencing human physiology, metabolism, nutrition and immune function. It is now widely accepted that perturbations of this close partnership results in the pathogenesis of several major diseases with increasing evidence highlighting their role outside of the intestinal tract. The intimate proximity and circulatory loop of the liver and the gut has attracted significant attention regarding the role of the microbiota in the development and progression of liver disease. Here we give an overview of the interaction between the microbiota and the immune system and focus on their convincing role in both the propagation and treatment of liver disease.

Regulatory T Cells: Serious Contenders in the Promise for Immunological Tolerance in Transplantation

Regulatory T cells (Tregs) play an important role in immunoregulation and have been shown in animal models to promote transplantation tolerance and curb autoimmunity following their adoptive transfer. The safety and potential therapeutic efficacy of these cells has already been reported in Phase I trials of bone-marrow transplantation and type I diabetes, the success of which has motivated the broadened application of these cells in solid-organ transplantation. Despite major advances in the clinical translation of these cells, there are still key questions to be addressed to ensure that Tregs attest their reputation as ideal candidates for tolerance induction. In this review, we will discuss the unique traits of Tregs that have attracted such fame in the arena of tolerance induction. We will outline the protocols used for their ex vivo expansion and discuss the future directions of Treg cell therapy. In this regard, we will review the concept of Treg heterogeneity, the desire to isolate and expand a functionally superior Treg population and report on the effect of differing culture conditions. The relevance of Treg migratory capacity will also be discussed together with methods of in vivo visualization of the infused cells. Moreover, we will highlight key advances in the identification and expansion of antigen-specific Tregs and discuss their significance for cell therapy application. We will also summarize the clinical parameters that are of importance, alongside cell manufacture, from the choice of immunosuppression regimens to the number of injections in order to direct the success of future efficacy trials of Treg cell therapy. Years of research in the field of tolerance have seen an accumulation of knowledge and expertise in the field of Treg biology. This perpetual progression has been the driving force behind the many successes to date and has put us now within touching distance of our ultimate success, immunological tolerance.

Activated regulatory T-cells attenuate myocardial ischaemia/reperfusion injury through a CD39-dependent mechanism

Regulatory T-cells (Tregs) are generally regarded as key immunomodulators that maintain immune tolerance and counteract tissue damage in a variety of immune-mediated disorders. However, its role in myocardial ischaemia/reperfusion injury (MIRI) remains unknown. The purpose of the present study was to determine whether Tregs exert a beneficial effect on mouse MIRI. We examined the role of Tregs in murine MIRI by depletion using 'depletion of regulatory T-cell' (DEREG) mice and adoptive transfer using Forkhead box P3 (Foxp3)-GFP knockin mice and the mechanisms of cardio protection were further studied in vivo and in vitro. Tregs rapidly accumulated in murine hearts following MIRI. Selective depletion of Tregs in the DEREG mouse model resulted in aggravated MIRI. In contrast, the adoptive transfer of in vitro-activated Tregs suppressed MIRI, whereas freshly isolated Tregs had no effect. Mechanistically, activated Treg-mediated protection against MIRI was not abrogated by interleukin (IL)-10 or transforming growth factor (TGF)-β1 inhibition but was impaired by the genetic deletion of cluster of differentiation 39 (CD39). Moreover, adoptive transfer of in vitro-activated Tregs attenuated cardiomyocyte apoptosis, activated a pro-survival pathway involving Akt and extracellular-signal-regulated kinase (ERK) and inhibited neutrophil infiltration, which was compromised by CD39 deficiency. Finally, the peripheral blood mononuclear cells of acute myocardial infarction (AMI) patients after primary percutaneous coronary intervention (PCI) revealed a decrease in CD4+CD25+CD127low Tregs and a relative increase in CD39+ cells within the Treg population. In conclusion, our data validated a protective role for Tregs in MIRI. Moreover, in vitro-activated Tregs ameliorated MIRI via a CD39-dependent mechanism, representing a putative therapeutic strategy.

Regulatory and effector T cells changes in remission and resistant state of childhood nephrotic syndrome

Idiopathic minimal change disease is a disorder of T-cell dysfunction. The relative predominance of regulatory T cells (Tregs), Th1, and Th2 cells in nephrotic syndrome (NS) remains controversial. Imbalance in peripheral blood regulatory and effector T cells (Teff) are linked to cell mediated immune response and may be associated with steroid response in NS. Peripheral blood CD4 + CD25 + FoxP3 + (Tregs), CD4 + IFN-γ⁺ (Th1), and CD4 + IL-4 + (Th2) lymphocytes were analyzed in 22 steroid-sensitive NS (SSNS) patients in sustained remission, 21 steroid-resistant NS (SRNS) and 14 healthy controls. The absolute percentage values and ratio of Th1/Tregs, Th2/Tregs, and Th1/Th2 were compared between SSNS, SRNS and control subjects. The percentage of Tregs was lower in SRNS patients (P = 0.001) compared with that of SSNS and healthy control. The percentage of Th1 cells was higher in SRNS (P = 0.001) compared to that of SSNS patients; however, it was similar to healthy controls (P = 1.00). The percentage of Th2 cells in SRNS (P = 0.001) was higher as compared to SSNS and controls. The ratio of Th1/Treg cells in SRNS (P = 0.001) was higher as compared to SSNS patients and controls. The ratio of Th2/Treg was also higher in SRNS as compared to SSNS and controls. The ratio of Th1/Th2 cells in SSNS, SRNS, and healthy controls were similar. The cytokines secretion complemented the change in different T-cell subtypes in SSNS, SRNS and healthy controls. However, the IFN-γ secretion in healthy controles was low inspite of similar percentage of Th1 cells among SRNS cases. We conclude that greater ratio of Tregs compared to that Th1 and Th2 favor steroid sensitivity and reverse ratio results in to SRNS. The difference in ratio is related to pathogenesis or it can be used as marker to predict steroid responsiveness needs further evaluation.

All-trans retinoic acid and rapamycin synergize with transforming growth factor-β1 to induce regulatory T cells but confer different migratory capacities

Tregs play important roles in maintaining immune homeostasis, and thus, therapies based on Treg are promising candidates for the treatment for a variety of immune-mediated disorders. These therapies, however, face the significant challenge of obtaining adequate numbers of Tregs from peripheral blood that maintains suppressive function following extensive expansion. Inducing Tregs from non-Tregs offers a viable alternative. Different methods to induce Tregs have been proposed and involve mainly treating cells with TGF-β-iTreg. However, use of TGF-β alone is not sufficient to induce stable Tregs. ATRA or rapa has been shown to synergize with TGF-β to induce stable Tregs. Whereas TGF-β plus RA-iTregs have been well-described in the literature, the phenotype, function, and migratory characteristics of TGF-β plus rapa-iTreg have yet to be elucidated. Herein, we describe the phenotype and function of mouse rapa-iTreg and reveal that these cells differ in their in vivo homing capacity when compared with mouse RA-iTreg and mouse TGF-β-iTreg. This difference in migratory activity significantly affects the therapeutic capacity of each subset in a mouse model of colitis. We also describe the characteristics of iTreg generated in the presence of TGF-β, RA, and rapa.

Whole-body imaging of adoptively transferred T cells using magnetic resonance imaging, single photon emission computed tomography and positron emission tomography techniques, with a focus on regulatory T cells

Cell-based therapies using natural or genetically modified regulatory T cells (T(regs)) have shown significant promise as immune-based therapies. One of the main difficulties facing the further advancement of these therapies is that the fate and localization of adoptively transferred T(regs) is largely unknown. The ability to dissect the migratory pathway of these cells in a non-invasive manner is of vital importance for the further development of in-vivo cell-based immunotherapies, as this technology allows the fate of the therapeutically administered cell to be imaged in real time. In this review we will provide an overview of the current clinical imaging techniques used to track T cells and T(regs) in vivo, including magnetic resonance imaging (MRI) and positron emission tomography (PET)/single photon emission computed tomography (SPECT). In addition, we will discuss how the finding of these studies can be used, in the context of transplantation, to define the most appropriate T(reg) subset required for cellular therapy.

How can we cure a heart "in flame"? A translational view on inflammation in heart failure

The prevalence of chronic heart failure is still increasing making it a major health issue in the 21st century. Tremendous evidence has emerged over the past decades that heart failure is associated with a wide array of mechanisms subsumed under the term “inflammation”. Based on the great success of immuno-suppressive treatments in auto-immunity and transplantation, clinical trials were launched targeting inflammatory mediators in patients with chronic heart failure. However, they widely lacked positive outcomes. The failure of the initial study program directed against tumor necrosis factor-α led to the search for alternative therapeutic targets involving a broader spectrum of mechanisms besides cytokines. We here provide an overview of the current knowledge on immune activation in chronic heart failure of different etiologies, summarize clinical studies in the field, address unresolved key questions, and highlight some promising novel therapeutic targets for clinical trials from a translational basic science and clinical perspective.

Multiple unit pooled umbilical cord blood is a viable source of therapeutic regulatory T cells

BACKGROUND

Regulatory T cells (Treg) are potentially a useful therapeutic option for the treatment of immunopathological conditions including graft-versus-host disease. Umbilical cord blood (UCB) offers certain advantages over adult peripheral blood (APB) as a source of Treg for cellular therapy but yields far fewer Treg per unit. Pooling of Treg from multiple donors may overcome this challenge.

METHODS

In this study, we assessed the in vitro and in vivo efficacy of multiple donor pooled UCB or APB-derived Treg.

RESULTS

In vitro, pooled freshly isolated UCB-derived Treg were as suppressive as APB-derived Treg. However, in a mouse model of human skin allodestruction, pooled UCB-derived Treg were more potent at suppressing alloresponses and prolonging skin survival compared with pooled APB-derived Treg. Improved survival of UCB Treg in an in vivo cell survival assay and their lower expression of human leukocyte antigen-ABC suggested that lower immunogenicity may account for their superior efficacy in vivo.

CONCLUSION

Multiple-unit UCB is therefore a viable source of human Treg for cellular therapy, and pooling of Treg from multiple donors offers a useful strategy for achieving required therapeutic doses.

Synapse-directed delivery of immunomodulators using T-cell-conjugated nanoparticles

Regulating molecular interactions in the T-cell synapse to prevent autoimmunity or, conversely, to boost anti-tumor immunity has long been a goal in immunotherapy. However, delivering therapeutically meaningful doses of immune-modulating compounds into the synapse represents a major challenge. Here, we report that covalent coupling of maleimide-functionlized nanoparticles (NPs) to free thiol groups on T-cell membrane proteins enables efficient delivery of compounds into the T-cell synapse. We demonstrate that surface-linked NPs are rapidly polarized toward the nascent immunological synapse (IS) at the T-cell/APC contact zone during antigen recognition. To translate these findings into a therapeutic application we tested the NP delivery of NSC-87877, a dual inhibitor of Shp1 and Shp2, key phosphatases that downregulate T-cell receptor activation in the synapse, in the context of adoptive T cell therapy of cancer. Conjugating NSC-87877-loaded NPs to the surface of tumor-specific T cells just prior to adoptive transfer into mice with advanced prostate cancer promoted a much greater T-cell expansion at the tumor site, relative to co-infusing the same drug dose systemically, leading to enhanced survival of treated animals. In summary, our studies support the application of T-cell-linked synthetic NPs as efficient drug delivery vehicles into the IS, as well as the broad applicability of this new paradigm for therapeutically modulating signaling events at the T-cell/APC interface.

Double negative regulatory T cells in transplantation and autoimmunity: recent progress and future directions

T lymphocytes bearing the αβ T cell receptor (TCR) but lacking CD4, CD8, and markers of natural killer (NK) cell differentiation are known as 'double-negative' (DN) T cells and have been described in both humans and rodent models. We and others have shown that DN T cells can act as regulatory T cells (Tregs) that are able to prevent allograft rejection, graft-versus-host disease, and autoimmune diabetes. In the last few years, new data have revealed evidence of DN Treg function in vivo in rodents and humans. Moreover, significant advances have been made in the mechanisms by which DN Tregs target antigen-specific T cells. One major limitation of the field is the lack of a specific marker that can be used to distinguish truly regulatory DN T cells (DN Tregs) from non-regulatory ones, and this is the central challenge in the coming years. Here, we review recent progress on the role of DN Tregs in transplantation and autoimmunity, and their mechanisms of action. We also provide some perspectives on how DN Tregs compare with Foxp3(+) Tregs.

Harnessing regulatory T cells for transplant tolerance in the clinic through mTOR inhibition: myth or reality?

PURPOSE OF REVIEW

The inhibition of mTOR promotes immune tolerance in mouse models of transplantation, by favoring the expansion of regulatory T cells over effector T cells. However, attempts at inducing immune tolerance with the mTOR inhibitor (mTOR-I) in humans have so far failed. We herein review the immunological obstacles that need to be overcome in order to translate mTOR-I-related tolerogenic properties into the clinic.

RECENT FINDINGS

Our knowledge of regulatory T-cell biology has exploded over the past few years, providing clues to explain the complex impact of prolonged mTOR inhibition on the biology of regulatory T cells. Furthermore, recent data have shed light on the unexpected pro-inflammatory burst observed in some transplant recipients treated with mTOR-I. We propose that the exposure of an organism to pathogens determines the immunodominant effect of mTOR-I, altering the immune system from a state of tolerance in inbred animals to a state of infection-triggered enhanced inflammation in humans.

SUMMARY

Recent advances in the understanding of the pleiotropic effects of mTOR-I on the immune system are paving the way to new therapeutic avenues. Future mTOR-I-based tolerogenic protocols should counter the mTOR-I-related inflammation in order to selectively promote expansion of stable regulatory T cells. We herein envisage promising therapeutic perspectives.

Controlled release formulations of IL-2, TGF-β1 and rapamycin for the induction of regulatory T cells

The absence of regulatory T cells (Treg) is a hallmark for a wide variety of disorders such as autoimmunity, dermatitis, periodontitis and even transplant rejection. A potential treatment option for these disorders is to increase local Treg numbers. Enhancing local numbers of Treg through in situ Treg expansion or induction could be a potential treatment option for these disorders. Current methods for in vivo Treg expansion rely on biologic therapies, which are not Treg-specific and are associated with many adverse side-effects. Synthetic formulations capable of inducing Treg could be an alternative strategy to achieve in situ increase in Treg numbers. Here we report the development and in vitro testing of a Treg-inducing synthetic formulation that consists of controlled release vehicles for IL-2, TGF-β and rapamycin (a combination of cytokines and drugs that have previously been reported to induce Treg). We demonstrate that IL-2, TGF-β and rapamycin (rapa) are released over 3-4weeks from these formulations. Additionally, Treg induced in the presence of these formulations expressed the canonical markers for Treg (phenotype) and suppressed naïve T cell proliferation (function) at levels similar to soluble factor induced Treg as well as naturally occurring Treg. Most importantly, we show that these release formulations are capable of inducing FoxP3(+) Treg in human cells in vitro. In conclusion, our data suggest that controlled release formulations of IL-2, TGF-β and rapa can induce functional Treg in vitro with the potential to be developed into an in vivo Treg induction and expansion therapy.

Ex vivo IL-1 receptor type I expression in human CD4+ T cells identifies an early intermediate in the differentiation of Th17 from FOXP3+ naive regulatory T cells

IL-17-producing CD4(+) Th (Th17) cells are a unique subset of proinflammatory cells expressing the retinoic acid-related orphan receptor γt and associated with different forms of inflammatory autoimmune pathologies. The development of Th17 cells, mediated by TGF-β and IL-1, is closely related to that of FOXP3(+) suppressor/regulatory T cells (Treg). In this study, we report that ex vivo expression of IL-1RI in human circulating CD4(+) T cells identifies a subpopulation of FOXP3(+) Treg that coexpress retinoic acid-related orphan receptor γt, secrete IL-17, and are highly enriched among CCR7(+) central memory cells. Consistent with the concept that IL-1RI expression in Treg identifies a subpopulation at an early stage of differentiation, we show that, in Th17 populations differentiated in vitro from natural naive FOXP3(+) Treg, IL-1RI(+) IL-17-secreting cells are central memory cells, whereas IL-1RI(-) cells secreting IL-17 are effector memory cells. Together with the absence of detectable IL-1RI and IL-17 expression in resting naive CD4(+) T cells, these data identify circulating CCR7(+) Treg expressing IL-1RI ex vivo as early intermediates along an IL-1-controlled differentiation pathway leading from naive FOXP3(+) Treg to Th17 effectors. We further show that, whereas IL-1RI(+) central memory Treg respond to stimulation in the presence of IL-1 by generating IL-17-secreting effectors, a significant fraction of them maintain FOXP3 expression, consistent with an important role of this population in maintaining the Treg/Th17 memory pool in vivo.

Isolation, expansion and functional assessment of CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients awaiting kidney transplantation

BACKGROUND

The immunosuppressive properties of regulatory T cells have emerged as an attractive tool for the development of immunotherapies in various disease contexts, e.g. to treat transplantation induced immune reactions. This paper focuses on the process of obtaining and functionally characterizing CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients awaiting kidney transplantation.

METHODS

From October 2010 to March 2011 uremic patients awaiting living donor kidney transplantation, and their corresponding kidney donors, were enrolled in the study. A total of seven pairs were included. Isolation of CD4+CD25+FoxP3+ regulatory T cells was performed by magnetic activated cell sorting of peripheral blood mononuclear cells obtained from the uremic patients. Donor specific Tr1 cells were differentiated by repetitive stimulation of immature CD4+ T cells with immature dendritic cells, with the T cells coming from the future kidney recipients and the dendritic cells from the corresponding kidney donors. Cells were then expanded and functionally characterized by the one-way mixed leukocyte reaction and assessment of IL-10 production. Phenotypic analysis was performed by flow cytometry.

RESULTS

The fraction of CD4+CD25+FoxP3+ regulatory T cells after expansion varied from 39.1 to 50.4% and the cells retained their ability to substantially suppress the mixed leukocyte reaction in all but one patient (3.8-19.2% of the baseline stimulated leukocyte activity, p<0.05). Tr1 cells were successfully differentiated from all but one patient and produced high levels of IL-10 when stimulated with immature dendritic cells (1,275-11,038% of the baseline IL-10 secretion, p<0.05).

CONCLUSION

It is practically feasible to obtain and subsequently expand CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients without loss of function as assessed by in vitro analyses. This forms a base for adoptive regulatory T cell therapy in the setting of living donor kidney transplantation.

Human regulatory T cells with alloantigen specificity are more potent inhibitors of alloimmune skin graft damage than polyclonal regulatory T cells

Graft rejection by the immune system is a major cause of transplant failure. Lifelong immunosuppression decreases the incidence of graft rejection; however, nonspecific immunosuppression results in increased susceptibly to infection and cancer. Regulatory T cells (T(regs)), which suppress the activation of the immune system and induce tolerance, are currently under evaluation for use in clinical transplantation. Ex vivo expanded polyclonal T(regs) that are introduced into transplant recipients alter the balance of T effector cells to T(regs); however, experimental data suggest that alloantigen-specific T(regs) would be more effective at preventing graft rejection. We have developed a method to enrich alloantigen-specific human T(regs) based on the coexpression of activation markers, CD69 and CD71. These T(regs) could be readily expanded in vitro and demonstrated potent antigen-specific suppression. In a humanized mouse model of alloimmune-mediated injury of human skin grafts, alloantigen-specific T(regs) resulted in a significant reduction in clinically relevant indicators of dermal tissue injury when compared with polyclonal T(regs), restoring a histology comparable to healthy skin. This method of human allospecific T(reg) selection should be scalable to the clinic. The improved in vivo efficacy of alloantigen-specific T(regs) over polyclonal T(regs) shown here suggests that generating "customized" T(regs) with defined anti-donor allospecificities may improve current practice in clinical immunotherapy.

Induction of tolerance to parental parathyroid grafts using allogeneic thymus tissue in patients with DiGeorge anomaly

DiGeorge anomaly can affect both thymic and parathyroid function. Although athymia is corrected by allogeneic thymus transplantation, treatment options for hypoparathyroidism have been unsatisfactory. Parathyroid transplantation offers the potential for definitive cure but remains challenging because of graft rejection. Some allogeneic parathyroid grafts have functioned in adult recipients in the context of immunosuppression for renal transplantation. Other efforts have attempted to reduce the allogenicity of the parathyroid grafts through manipulation of the parathyroid tissues before transplantation (by using encapsulation or special culture techniques). Recently, we demonstrated the efficacy of parental parathyroid transplantation when combined with allogeneic thymus transplantation in an infant with complete DiGeorge anomaly. The recipient developed tolerance toward the parathyroid donor. The parathyroid graft has functioned for 5 years after transplantation without the need for continued immunosuppression or calcium supplementation. We observed that matching of the allogeneic thymus graft to the parathyroid donor HLA class II alleles that are unshared with the recipient appears to be associated with the induction of tolerance toward the parathyroid graft. Further work is needed to determine the optimal means for using combined allogeneic thymus and parental parathyroid transplantation to correct hypoparathyroidism in patients with both complete and partial DiGeorge anomaly.