Moving to tolerance: clinical application of T regulatory cells

Reduced immunomodulatory metabolite concentrations in peri-transplant fecal samples from heart allograft recipients

Background

Emerging evidence is revealing the impact of the gut microbiome on hematopoietic and solid organ transplantation. Prior studies postulate that this influence is mediated by bioactive metabolites produced by gut-dwelling commensal bacteria. However, gut microbial metabolite production has not previously been measured among heart transplant (HT) recipients.

Methods

In order to investigate the potential influence of the gut microbiome and its metabolites on HT, we analyzed the composition and metabolite production of the fecal microbiome among 48 HT recipients at the time of HT.

Results

Compared to 20 healthy donors, HT recipients have significantly reduced alpha, i.e. within-sample, microbiota diversity, with significantly lower abundances of key anaerobic commensal bacteria and higher abundances of potentially pathogenic taxa that have been correlated with adverse outcomes in other forms of transplantation. HT recipients have a wide range of microbiota-derived fecal metabolite concentrations, with significantly reduced levels of immune modulatory metabolites such as short chain fatty acids and secondary bile acids compared to healthy donors. These differences were likely due to disease severity and prior antibiotic exposures but were not explained by other demographic or clinical factors.

Conclusions

Key potentially immune modulatory gut microbial metabolites are quantifiable and significantly reduced among HT recipients compared to healthy donors. Further study is needed to understand whether this wide range of gut microbial dysbiosis and metabolite alterations impact clinical outcomes and if they can be used as predictive biomarkers or manipulated to improve transplant outcomes.

Linked sensitization by memory CD4+ T cells prevents costimulation blockade–induced transplantation tolerance

Dominant infectious tolerance explains how brief tolerance-inducing therapies result in lifelong tolerance to donor antigens and “linked” third-party antigens, while recipient sensitization and ensuing immunological memory prevent the successful induction of transplant tolerance. In this study, we juxtapose these 2 concepts to test whether mechanisms of dominant infectious tolerance can control a limited repertoire of memory T and B cells. We show that sensitization to a single donor antigen is sufficient to prevent stable transplant tolerance, rendering it unstable. Mechanistic studies revealed that recall antibody responses and memory CD8⁺ T cell expansion were initially controlled, but memory CD4⁺Foxp3^– T cell (Tconv) responses were not. Remarkably, naive donor-specific Tconvs at tolerance induction also acquired a resistance to tolerance, proliferating and acquiring a phenotype similar to memory Tconvs. This phenomenon of “linked sensitization” underscores the challenges of reprogramming a primed immune response toward tolerance and identifies a potential therapeutic checkpoint for synergizing with costimulation blockade to achieve transplant tolerance in the clinic.

Cell therapy in transplantation: A comprehensive review of the current applications of cell therapy in transplant patients with the focus on Tregs, CAR Tregs, and Mesenchymal stem cells

Organ transplantation is a practical treatment for patients with end-stage organ failure. Despite the advances in short-term graft survival, long-term graft survival remains the main challenge considering the increased mortality and morbidity associated with chronic rejection and the toxicity of immunosuppressive drugs. Since a novel therapeutic strategy to induce allograft tolerance seems urgent, focusing on developing novel and safe approaches to prolong graft survival is one of the main goals of transplant investigators. Researchers in the field of organ transplantation are interested in suppressing or optimizing the immune responses by focusing on immune cells including mesenchymal stem cells (MSCs), polyclonal regulatory Tcells (Tregs), and antigen-specific Tregs engineered with chimeric antigen receptors (CAR Tregs). We review the mechanistic pathways, phenotypic and functional characteristics of these cells, and their promising application in organ transplantation.

TNF-TNFR2 Signal Plays a Decisive Role in the Activation of CD4+Foxp3+ Regulatory T Cells: Implications in the Treatment of Autoimmune Diseases and Cancer

The puzzling biphasic or dual roles of tumor necrosis factor α (TNF) in the inflammatory and immune responses are likely to be mediated by distinct signaling pathways transduced by one of its two receptors, e.g., TNF receptor type I (TNFR1) and TNF receptor type II (TNFR2). Unlike TNFR1 that is ubiquitously expressed on almost all types of cells, the expression of TNFR2 is rather restricted to certain types of cells, such as T lymphocytes. There is now compelling evidence that TNFR2 is preferentially expressed by CD4⁺Foxp3⁺ regulatory T cells (Tregs), and TNFR2 plays a decisive role in the activation, expansion, in vivo function, and phenotypical stability of Tregs. In this chapter, the current understanding of the molecular basis and signaling pathway of TNF-TNFRs signal is introduced. Latest studies that have further supported and substantiated the pivotal role of TNF-TNFR2 interaction in Tregs biology and its molecular basis are discussed. The research progress regarding TNFR2-targeting treatment for autoimmune diseases and cancer is analyzed. Future study should focus on the further understanding of molecular mechanism underlying Treg-stimulatory effect of TNFR2 signal, as well as on the translation of research findings into therapeutic benefits of human patients with autoimmune diseases, allergy, allograft rejection, and cancer.

Regulatory T cells: A potential weapon to combat COVID-19?

Since the end of December 2019, a novel coronavirus SARS-CoV-2 began to spread, an infection disease termed COVID-19. The virus has spread throughout the world in a short period of time, resulting in a pandemic. The number of reported cases in global reached 5 695 596 including 352 460 deaths, as of May 27, 2020. Due to the lack of effective treatment options for COVID-19, various strategies are being tested. Recently, pathologic studies conducted by two teams in China revealed immunopathologic abnormalities in lung tissue. These results have implications for immunotherapy that could offer a novel therapy strategy for combating lethal viral pneumonia. This review discusses the clinical and pathological features of COVID-19, the roles of immune cells in pathological processes, and the possible avenues for induction of immunosuppressive T regulatory cells attenuating lung inflammation due to viral infection. It is our hope that these proposals may both be helpful in understanding the novel features of SARS-CoV-2 pneumonia as well as providing new immunological strategies for treating the severe sequelae of disease manifestations seen in people infected with SARS-CoV-2.

FTY720 Regulates Mitochondria Biogenesis in Dendritic Cells to Prevent Kidney Ischemic Reperfusion Injury

Dendritic cells (DCs) are central in regulating immune responses of kidney ischemia-reperfusion injury (IRI), and strategies to alter DC function may provide new therapeutic opportunities. Sphingosine 1-phosphate (S1P) modulates immunity through binding to its receptors (S1P1-5), and protection from kidney IRI occurs in mice treated with S1PR agonist, FTY720 (FTY). We tested if ex vivo propagation of DCs with FTY could be used as cellular therapy to limit the off-target effects associated with systemic FTY administration in kidney IRI. DCs have the ability of regulate innate and adaptive responses and we posited that treatment of DC with FTY may underlie improvements in kidney IRI. Herein, it was observed that treatment of bone marrow derived dendritic cells (BMDCs) with FTY induced mitochondrial biogenesis, FTY-treated BMDCs (FTY-DCs) showed significantly higher oxygen consumption rate and ATP production compared to vehicle treated BMDCs (Veh-DCs). Adoptive transfer of FTY-DCs to mice 24 h before or 4 h after IRI significantly protected the kidneys from injury compared to mice treated with Veh-DCs. Additionally, allogeneic adoptive transfer of C57BL/6J FTY-DCs into BALB/c mice equally protected the kidneys from IRI. FTY-DCs propagated from S1pr1-deficient DCs derived from CD11cCreS1pr1^fl/fl mice as well as blunting mitochondrial oxidation in wildtype (WT) FTY-DCs prior to transfer abrogated the protection observed by FTY-DCs. We queried if DC mitochondrial content alters kidney responses after IRI, a novel but little studied phenomenon shown to be integral to regulation of the immune response. Transfer of mitochondria rich FTY-DCs protects kidneys from IRI as transferred FTY-DCs donated their mitochondria to recipient splenocytes (i.e., macrophages) and prior splenectomy abrogated this protection. Adoptive transfer of FTY-DCs either prior to or after ischemic injury protects kidneys from IRI demonstrating a potent role for donor DC-mitochondria in FTY's efficacy. This is the first evidence, to our knowledge, that DCs have the potential to protect against kidney injury by donating mitochondria to splenic macrophages to alter their bioenergetics thus making them anti-inflammatory. In conclusion, the results support that ex vivo FTY720-induction of the regulatory DC phenotype could have therapeutic relevance that can be preventively infused to reduce acute kidney injury.

Donor-specific chimeric antigen receptor Tregs limit rejection in naive but not sensitized allograft recipients

Cell therapy with autologous donor-specific regulatory T cells (Tregs) is a promising strategy to minimize immunosuppression in transplant recipients. Chimeric antigen receptor (CAR) technology has recently been used successfully to generate donor-specific Tregs and overcome the limitations of enrichment protocols based on repetitive stimulations with alloantigens. However, the ability of CAR-Treg therapy to control alloreactivity in immunocompetent recipients is unknown. We first analyzed the effect of donor-specific CAR Tregs on alloreactivity in naive, immunocompetent mice receiving skin allografts. Tregs expressing an irrelevant or anti-HLA-A2-specific CAR were administered to Bl/6 mice at the time of transplanting an HLA-A2⁺ Bl/6 skin graft. Donor-specific CAR-Tregs, but not irrelevant-CAR Tregs, significantly delayed skin rejection and diminished donor-specific antibodies (DSAs) and frequencies of DSA-secreting B cells. Donor-specific CAR-Treg-treated mice also had a weaker recall DSA response, but normal responses to an irrelevant antigen, demonstrating antigen-specific suppression. When donor-specific CAR Tregs were tested in HLA-A2-sensitized mice, they were unable to delay allograft rejection or diminish DSAs. The finding that donor-specific CAR-Tregs restrain de novo but not memory alloreactivity has important implications for their use as an adoptive cell therapy in transplantation.

Treg expression of CIS suppresses allergic airway inflammation through antagonizing an autonomous TH2 program

Maintenance of regulatory T (Treg) cells is crucial for the regulatory function of Treg cells in immune homeostasis and self-tolerance; however, the detailed underlying mechanisms remain elusive. In the current study, we found that the cytokine suppressor CIS (cytokine induced SH-2 protein) is required for maintenance of Treg cell identity. Mice with Treg-specific Cis-deficiency displayed aggravated experimental allergic asthma, and in adulthood, developed splenomegaly, lymphadenopathy and spontaneous eosinophilic airway inflammation, accompanied by accumulation of effector memory helper T (TH) cells. Cis-deficiency led to the loss of Foxp3 expression and the decrease in suppressive function of Treg cells. Cis-deficient Treg cells expressed TH2 cell signature genes, Gata3, Irf4 and Il4, and excessive interleukin-4-signal transducer and activator of transcription 6 (IL-4-STAT6) signals resulted in repressive chromatin modification in the Foxp3 locus and permissive modification in the Il4 loci. In vitro, blockade of IL-4 restored the expression of Foxp3 and the suppressive function of inducible Treg (iTreg) cells. Thus, we identified a novel feedback loop in stabilization of Treg cells and suppression of TH2-type inflammation in a Treg-intrinsic manner.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Bioprinting an Artificial Pancreas for Type 1 Diabetes

PURPOSE OF REVIEW

Pancreatic islet cell transplantation is currently the only curative cell therapy for type 1 diabetes mellitus. However, its potential to treat many more patients is limited by several challenges. The emergence of 3D bioprinting technology from recent advances in 3D printing, biomaterials, and cell biology has provided the means to overcome these challenges.

RECENT FINDINGS

3D bioprinting allows for the precise fabrication of complex 3D architectures containing spatially distributed cells, biomaterials (bioink), and bioactive factors. Different strategies to capitalize on this ability have been investigated for the 3D bioprinting of pancreatic islets. In particular, with co-axial bioprinting technology, the co-printability of islets with supporting cells such as endothelial progenitor cells and regulatory T cells, which have been shown to accelerate revascularization of islets and improve the outcome of various transplantations, respectively, has been achieved. 3D bioprinting of islets for generation of an artificial pancreas is a newly emerging field of study with a vast potential to improve islet transplantation.

Engineering human stellate cells for beta cell replacement therapy promotes in vivo recruitment of regulatory T cells

Type 1 diabetes (T1D) is an autoimmune disease characterized by destruction of pancreatic β cells. One of the promising therapeutic approaches in T1D is the transplantation of islets; however, it has serious limitations. To address these limitations, immunotherapeutic strategies have focused on restoring immunologic tolerance, preventing transplanted cell destruction by patients’ own immune system. Macrophage-derived chemokines such as chemokine-ligand-22 (CCL22) can be utilized for regulatory T cell (Treg) recruitment and graft tolerance. Stellate cells (SCs) have various immunomodulatory functions: recruitment of Tregs and induction of T-cell apoptosis. Here, we designed a unique immune-privileged microenvironment around implantable islets through overexpression of CCL22 proteins by SCs. We prepared pseudoislets with insulin-secreting mouse insulinoma-6 (MIN6) cells and human SCs as a model to mimic naive islet morphology. Our results demonstrated that transduced SCs can secrete CCL22 and recruit Tregs toward ​the implantation site in vivo. This study is promising to provide a fundamental understanding of SC-islet interaction and ligand synthesis and transport from SCs at the graft site for ensuring local immune tolerance. Our results also establish a new paradigm for creating tolerable grafts for other chronic diseases such as diabetes, anemia, and central nervous system (CNS) diseases, and advance the science of graft tolerance.

Immune Tolerance and Rejection in Organ Transplantation

In this chapter, we describe the history of transplantation, the multiple cell types, and mechanisms that are involved in rejection and tolerance of a transplanted organ, as well as summarize the common and promising new therapeutics used in transplant patients.

Intradermal injection of low dose human regulatory T cells inhibits skin inflammation in a humanized mouse model

Recent regulatory T cell (Treg) based clinical trials support their therapeutic potential in transplantation and auto-inflammatory diseases. However, large numbers of Treg are needed to accomplish therapeutic efficacy. Local injection at the site of inflammation (targeted delivery) may lower the numbers needed for therapy. We evaluated if local delivery of low numbers of human Treg by intradermal injection was able to prevent skin inflammation, using the humanized mouse huPBL-SCID-huSkin allograft model. A dose of only 1 × 10⁵ freshly isolated, non expanded Treg injected intradermally in close proximity to the transplanted human skin prevented inflammation of the grafted tissue induced by 4 × 10⁷ IP injected human allogeneic PBMCs, (ratio Treg:PBMC = 1:400), as indicated by the inhibition of epidermal thickening, sustained Keratin-10 expression, the absence of Keratin-16 up regulation and prevention of human CD3+ T cell influx. A concomitant reduction of human T cells was observed in lymph nodes and spleen of the mice. Injection of Treg at the contralateral side was also shown to inhibit skin inflammation, suggesting that the inflammatory response was regulated both locally and systemically. In conclusion, local application of Treg may be an attractive way to suppress inflammation in vivo without the need for prior ex vivo expansion.

Targeting the epitope spreader Pep19 by naïve human CD45RA+ regulatory T cells dictates a distinct suppressive T cell fate in a novel form of immunotherapy

Purpose

Beyond the limited scope of non-specific polyclonal regulatory T cell (Treg)-based immunotherapy, which depends largely on serendipity, the present study explored a target Treg subset appropriate for the delivery of a novel epitope spreader Pep19 antigen as part of a sophisticated form of immunotherapy with defined antigen specificity that induces immune tolerance.

Methods

Human polyclonal CD4⁺CD25⁺CD127^lo− Tregs (127-Tregs) and naïve CD4⁺CD25⁺CD45RA⁺ Tregs (45RA-Tregs) were isolated and were stimulated with target peptide 19 (Pep19)-pulsed dendritic cells in a tolerogenic milieu followed by ex vivo expansion. Low-dose interleukin-2 (IL-2) and rapamycin were added to selectively exclude the outgrowth of contaminating effector T cells (Teffs). The following parameters were investigated in the expanded antigen-specific Tregs: the distinct expression of the immunosuppressive Treg marker Foxp3, epigenetic stability (demethylation in the Treg-specific demethylated region), the suppression of Teffs, expression of the homing receptors CD62L/CCR7, and CD95L-mediated apoptosis. The expanded Tregs were adoptively transferred into an NOD/scid/IL-2Rγ^−/− mouse model of collagen-induced arthritis.

Results

Epitope-spreader Pep19 targeting by 45RA-Tregs led to an outstanding in vitro suppressive T cell fate characterized by robust ex vivo expansion, the salient expression of Foxp3, high epigenetic stability, enhanced T cell suppression, modest expression of CD62L/CCR7, and higher resistance to CD95L-mediated apoptosis. After adoptive transfer, the distinct fate of these T cells demonstrated a potent in vivo immunotherapeutic capability, as indicated by the complete elimination of footpad swelling, prolonged survival, minimal histopathological changes, and preferential localization of CD4⁺CD25⁺ Tregs at the articular joints in a mechanistic and orchestrated way.

Conclusions

We propose human naïve CD4⁺CD25⁺CD45RA⁺ Tregs and the epitope spreader Pep19 as cellular and molecular targets for a novel antigen-specific Treg-based vaccination against collagen-induced arthritis.

Harnessing Advances in T Regulatory Cell Biology for Cellular Therapy in Transplantation

Cellular therapy with CD4FOXP3 T regulatory (Treg) cells is a promising strategy to induce tolerance after solid-organ transplantation or prevent graft-versus-host disease after transfer of hematopoietic stem cells. Treg cells currently used in clinical trials are either polyclonal, donor- or antigen-specific. Aside from variations in isolation and expansion protocols, however, most therapeutic Treg cell-based products are much alike. Ongoing basic science work has provided considerable new insight into multiple facets of Treg cell biology, including their stability, homing, and functional specialization; integrating these basic science discoveries with clinical efforts will support the development of next-generation therapeutic Treg cells with enhanced efficacy. In this review, we summarize recent advances in knowledge of how Treg cells home to lymphoid and peripheral tissues, and control antibody production and tissue repair. We also discuss newly appreciated pathways that modulate context-specific Treg cell function and stability. Strategies to improve and tailor Treg cells for cell therapy to induce transplantation tolerance are highlighted.

iPSC-Derived Regulatory Dendritic Cells Inhibit Allograft Rejection by Generating Alloantigen-Specific Regulatory T Cells

Regulatory dendritic cell (DCregs)-based immunotherapy is a potential therapeutic tool for transplant rejection. We generated DCregs from murine induced pluripotent stem cells (iPSCs), which could remain in a “stable immature stage” even under strong stimulation. Harnessing this characteristic, we hypothesized that iPS-DCregs worked as a negative vaccine to generate regulatory T cells (Tregs), and induced donor-specific allograft acceptance. We immunized naive CBA (H-2K^k) mice with B6 (H-2K^b) iPS-DCregs and found that Tregs (CD4⁺CD25⁺FOXP3⁺) significantly increased in CBA splenocytes. Moreover, immunized CBA recipients permanently accepted B6 cardiac grafts in a donor-specific pattern. We demonstrated mechanistically that donor-type iPS-DCregs triggered transforming growth factor β1 secretion, under which the donor-antigen peptides directed naive CD4⁺ T cells to differentiate into donor-specific FOXP3⁺ Tregs instead of into effector T cells in vivo. These findings highlight the potential of iPS-DCregs as a key cell therapy resource in clinical transplantation.

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iPS-DCregs keep in stable immature stage that makes them a powerful cellular vaccine

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Donor-type iPS-DCregs lead to permanent acceptance of allogeneic cardiac grafts

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iPS-DCregs reduce CTL and downregulate proinflammatory cytokine

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iPS-DCregs enhance Tregs transmigration capability in a TGF-β1-dependent manner

TLR3 or TLR4 Activation Enhances Mesenchymal Stromal Cell-Mediated Treg Induction via Notch Signaling

Mesenchymal stromal cells (MSCs) are the subject of numerous clinical trials, largely due to their immunomodulatory and tissue regenerative properties. Toll-like receptors (TLRs), especially TLR3 and TLR4, are highly expressed on MSCs and their activation can significantly modulate the immunosuppressive and anti-inflammatory functions of MSCs. While MSCs can recruit and promote the generation of regulatory T cells (Tregs), the effect of TLR activation on MSC-mediated Treg induction is unknown. In this study, we investigated the effect of ligand-mediated activation of TLR3 and TLR4 on Treg induction by human MSCs. We found that generation of Tregs in human CD4(+) lymphocyte and MSC cocultures was enhanced by either TLR3 or TLR4 activation of MSCs and that the increase was abolished by TLR3 and TLR4 gene-silencing. Augmented Treg induction by TLR-activated MSCs was cell contact-dependent and associated with increased gene expression of the Notch ligand, Delta-like 1. Moreover, inhibition of Notch signaling abrogated the augmented Treg levels in the MSC cocultures. Our data show that TLR3 or TLR4 activation of MSCs increases Treg induction via the Notch pathway and suggest new means to enhance the potency of MSCs for treating disorders with an underlying immune dysfunction, including steroid resistant acute graft-versus-host disease. Stem Cells 2017;35:265-275.

Tolerance in liver transplantation: Biomarkers and clinical relevance

Transplantation is the optimal treatment for end-stage organ failure, and modern immunosuppression has allowed important progress in short-term outcomes. However, immunosuppression poorly influences chronic rejection and elicits chronic toxicity in current clinical practice. Thus, a major goal in transplantation is to understand and induce tolerance. It is well established that human regulatory T cells expressing the transcription factor FoxP3 play important roles in the maintenance of immunological self-tolerance and immune homeostasis. The major regulatory T cell subsets and mechanisms of expansion that are critical for induction and long-term maintenance of graft tolerance and survival are being actively investigated. Likewise, other immune cells, such as dendritic cells, monocyte/macrophages or natural killer cells, have been described as part of the process known as "operational tolerance". However, translation of these results towards clinical practice needs solid tools to identify accurately and reliably patients who are going to be tolerant. In this way, a plethora of genetic and cellular biomarkers is raising and being validated worldwide in large multi-center clinical trials. Few of the studies performed so far have provided a detailed analysis of the impact of immunosuppression withdrawal on pre-existing complications derived from the long-term administration of immunosuppressive drugs and the side effects associated with them. The future of liver transplantation is aimed to develop new therapies which increase the actual low tolerant vs non-tolerant recipients ratio.

Overexpression of Fibrinogen-Like Protein 2 Promotes Tolerance in a Fully Mismatched Murine Model of Heart Transplantation

Fibrinogen-like protein 2 (FGL2) is an immunomodulatory protein that is expressed by regulatory T cells (Tregs). The objective of this study was to determine if recombinant FGL2 (rFGL2) treatment or constitutive FGL2 overexpression could promote transplant tolerance in mice. Although rFGL2 treatment prevented rejection of fully mismatched cardiac allografts, all grafts were rejected after stopping treatment. Next, we generated FGL2 transgenic mice (fgl2(Tg) ) that ubiquitously overexpressed FGL2. These mice developed normally and had no evidence of the autoimmune glomerulonephritis seen in fgl2(-/-) mice. Immune characterization showed fgl2(Tg) T cells were hypoproliferative to stimulation with alloantigens or anti-CD3 and anti-CD28 stimulation, and fgl2(Tg) Tregs had increased immunosuppressive activity compared with fgl2(+/+) Tregs. To determine if FGL2 overexpression can promote tolerance, we transplanted fully mismatched cardiac allografts into fgl2(Tg) recipients. Fifty percent of cardiac grafts were accepted indefinitely in fgl2(Tg) recipients without any immunosuppression. Tolerant fgl2(Tg) grafts had increased numbers and proportions of Tregs and tolerant fgl2(Tg) mice had reduced proliferation to donor but not third party antigens. These data show that tolerance in fgl2(Tg) recipients involves changes in Treg and T cell activity that contribute to a higher intragraft Treg-to-T cell ratio and acceptance of fully mismatched allografts.

Targeting Sirtuin-1 prolongs murine renal allograft survival and function

Current immunosuppressive medications used after transplantation have significant toxicities. Foxp3(+) T-regulatory cells can prevent allograft rejection without compromising protective host immunity. Interestingly, inhibiting the class III histone/protein deacetylase Sirtuin-1 can augment Foxp3(+) T-regulatory suppressive function through increasing Foxp3 acetylation. Here we determined whether Sirtuin-1 targeting can stabilize biological allograft function. BALB/c kidney allografts were transplanted into C57BL/6 recipients with a CD4-conditional deletion of Sirtuin-1 (Sirt1(fl/fl)CD4(cre)) or mice treated with a Sirtuin-1-specific inhibitor (EX-527), and the native kidneys removed. Blood chemistries and hematocrit were followed weekly. Sirt1(fl/fl)CD4(cre) recipients showed markedly longer survival and improved kidney function. Sirt1(fl/fl)CD4(cre) recipients exhibited donor-specific tolerance, accepted BALB/c, but rejected third-party C3H cardiac allografts. C57BL/6 recipients of BALB/c renal allografts that were treated with EX-527 showed improved survival and renal function at 1, but not 10 mg/kg/day. Pharmacologic inhibition of Sirtuin-1 also improved renal allograft survival and function with dosing effects having relevance to outcome. Thus, inhibiting Sirtuin-1 can be a useful asset in controlling T-cell-mediated rejection. However, effects on non-T cells that could adversely affect allograft survival and function merit consideration.

T regulatory cell chemokine production mediates pathogenic T cell attraction and suppression

T regulatory cells (Tregs) control immune homeostasis by preventing inappropriate responses to self and nonharmful foreign antigens. Tregs use multiple mechanisms to control immune responses, all of which require these cells to be near their targets of suppression; however, it is not known how Treg-to-target proximity is controlled. Here, we found that Tregs attract CD4+ and CD8+ T cells by producing chemokines. Specifically, Tregs produced both CCL3 and CCL4 in response to stimulation, and production of these chemokines was critical for migration of target T cells, as Tregs from Ccl3-/- mice, which are also deficient for CCL4 production, did not promote migration. Moreover, CCR5 expression by target T cells was required for migration of these cells to supernatants conditioned by Tregs. Tregs deficient for expression of CCL3 and CCL4 were impaired in their ability to suppress experimental autoimmune encephalomyelitis or islet allograft rejection in murine models. Moreover, Tregs from subjects with established type 1 diabetes were impaired in their ability to produce CCL3 and CCL4. Together, these results demonstrate a previously unappreciated facet of Treg function and suggest that chemokine secretion by Tregs is a fundamental aspect of their therapeutic effect in autoimmunity and transplantation.

The influence of experimental administration of low zearalenone doses on the expression of Th1 and Th2 cytokines and on selected subpopulations of lymphocytes in intestinal lymph nodes

The aim of this study was to characterize the immune response taking place in ileocecal lymph nodes (ICLN) in control (n=15) and zearalenone (ZEN)-treated (n=15) pigs. The experiment was carried out over 42 days; a dose of 0.1 mg kg-1 feed day-1 of ZEN was administered to the animals. The dose used in the experiment was at a level where no adverse effects are observed (NOAEL) in the ovaries, uterus and vagina. ICLN samples for analysis were collected on the 14th, 28th and 42nd day of the experiment. The analysis of cytokine concentration in the tissues showed that pigs treated with ZEN had an increased level of cytokines produced by helper Th1 lymphocytes (IL-2, IL-12 and IFN-γ) on the 28th day of the experiment. The level of cytokines produced by helper Th2 lymphocytes (IL-4 and IL-10) was characterized by a statistically non-significant upward trend, as compared with the control group. Flow cytometry showed a linear decrease in the percentage of CD21+ B, CD2+ T and CD4+CD8- T cells and an increase in the percentage of CD8+CD4- and TCRγδ + T cells in pigs treated with ZEN. Both ZEN and α-ZEL (α-zearalenone) concentrations increased over time in the liver, but only ZEN concentration increased in ICLN. The results obtained demonstrate that a NOAEL concentration of ZEN shifts the immune response in pig ICLN towards Th1/Th17, probably with a simultaneous activation of M1 macrophages. Moreover, we observed an increase in humoral cytokine secretion; this can be explained by a negative feedback loop and a phenotypic switch of macrophages from M1 to M2, as well as a switch of immune response from Th1 to Th2 type. ZEN can therefore influence the process of cytokine secretion and the percentage of lymphocytes in ileocecal lymph nodes.

Targeting Antigens to Dec-205 on Dendritic Cells Induces Immune Protection in Experimental Colitis in Mice

The endocytotic c-type lectin receptor DEC-205 is highly expressed on immature dendritic cells. In previous studies, it was shown that antigen-targeting to DEC-205 is a useful tool for the induction of antigen-specific Foxp3⁺ regulatory T cells and thereby can prevent inflammatory processes. However, whether this approach is sufficient to mediate tolerance in mucosal tissues like the gut is unknown. In this study, we established a new mouse model in which the adoptive transfer of naive hemagglutinin (HA)-specific CD4⁺Foxp3^– T cells into VILLIN-HA transgenic mice leads to severe colitis. To analyze if antigen-targeting to DEC-205 could protect against inflammation of the gut, VILLIN-HA transgenic mice were injected with an antibody–antigen complex consisting of the immunogenic HA_110–120 peptide coupled to an α-DEC-205 antibody (DEC-HA) before adoptive T cell transfer. DEC-HA-treated mice showed significantly less signs of intestinal inflammation as was demonstrated by reduced loss of body weight and histopathology in the gut. Strikingly, abrogated intestinal inflammation was mediated via the conversion of naive HA-specific CD4⁺Foxp3^– T cells into HA-specific CD4⁺Foxp3⁺ regulatory T cells. In this study, we provide evidence that antigen-targeting to DEC-205 can be utilized for the induction of tolerance in mucosal organs that are confronted with large numbers of exogenous antigens.

Expansion of Regulatory T Cells In Vitro and In Vivo by IL-33

Thymic-derived, regulatory T cells (Treg) represent a subset of CD4(+) T cells that are required for normal immune homeostasis and suppression of unwanted responses against self-antigens (Ags) that prevent autoimmunity. Their role as immune regulators and potent ability to suppress T cell responses has been the focus of intense investigations aimed at utilizing these cells therapeutically, particularly in the settings of autoimmunity and transplantation. Many methods for expanding Treg have been described; however, efforts to generate large numbers of Treg for use in vivo often compromise their suppressor function or rely on the induction of Treg rather than their expansion. Our recent studies have focused on the barrier tissue-derived cytokine IL-33, a recently described IL-1 family member. IL-33 has emerged as a multifunctional protein, with reported roles in driving potent Type 1 and Type 2 immunity, as well as facilitating profound Treg expansion in vitro and in vivo. IL-33-expanded Treg express the IL-33 receptor (R) ST2, and express classical markers associated with Treg phenotype and suppressor function. They suppress both CD4(+) and CD8(+) T cell proliferation and effector functions in vitro, and Treg expressing ST2 have been identified as important regulators of detrimental immune responses in vivo. In the present chapter, we detail methods for expanding significant numbers of Treg using IL-33 both in vitro and in vivo that may potentially be used to promote/maintain organ transplant tolerance or suppress autoimmunity.

Discarded Human Thymus Is a Novel Source of Stable and Long-Lived Therapeutic Regulatory T Cells

Regulatory T cell (Treg)-based therapy is a promising approach to treat many immune-mediated disorders such as autoimmune diseases, organ transplant rejection, and graft-versus-host disease (GVHD). Challenges to successful clinical implementation of adoptive Treg therapy include difficulties isolating homogeneous cell populations and developing expansion protocols that result in adequate numbers of cells that remain stable, even under inflammatory conditions. We investigated the potential of discarded human thymuses, routinely removed during pediatric cardiac surgery, to be used as a novel source of therapeutic Tregs. Here, we show that large numbers of FOXP3(+) Tregs can be isolated and expanded from a single thymus. Expanded thymic Tregs had stable FOXP3 expression and long telomeres, and suppressed proliferation and cytokine production of activated allogeneic T cells in vitro. Moreover, expanded thymic Tregs delayed development of xenogeneic GVHD in vivo more effectively than expanded Tregs isolated based on CD25 expression from peripheral blood. Importantly, in contrast to expanded blood Tregs, expanded thymic Tregs remained stable under inflammatory conditions. Our results demonstrate that discarded pediatric thymuses are an excellent source of therapeutic Tregs, having the potential to overcome limitations currently hindering the use of Tregs derived from peripheral or cord blood.

Clinical grade isolation of regulatory T cells from G-CSF mobilized peripheral blood improves with initial depletion of monocytes

Clinical isolation of circulating CD4(+)CD25(+) regulatory T cells (Tregs) from peripheral blood mononuclear cells is usually performed by CD4(+) cell negative selection followed by CD25(+) cell positive selection. Although G-CSF mobilized peripheral blood (G-PBSC) contains a high number of Tregs, a high number of monocytes in G-PBSC limits Treg isolation. Using a small scale device (MidiMACS, Miltenyi) we initially demonstrated that an initial depletion of monocytes would be necessary to obtaina separation of CD4(+)CD25(+)FoxP3(+)CD127(-) cells from G-PBSC (G-Tregs) with a consistent purity >70% and inhibitory activity of T cell alloreactivity in-vitro. We then validated the same approach in a clinical scale setting by separating G-Tregs with clinically available antibodies to perform a CD8(+)CD19(+)CD14(+) cell depletion followed by CD25(+) cell selection (2-step process) or by adding an initial CD14(+) cell depletion (3-step process) using a CliniMACS column. The 3-step approach resulted in a better purity (81±12% vs. 35±33%) and yield (66% vs. 39%). Clinically isolated G-Tregs were also FoxP3(+)CD127(dim) and functionally suppressive in-vitro. Our findings suggest that a better and more consistent purity of Tregs can be achieved from G-PBSC by an initial single depletion of monocytes prior to selection of CD4(+)CD25(+) cells.

TGF-β in tolerance, development and regulation of immunity

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The broader superfamily of TGF-β-like proteins is reviewed, and signaling pathways summarised.

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The role of TGF-β in the immune tolerance and control of infectious disease is discussed.

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The superfamily member AMH is involved in embryonic sexual differentiation.

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Helminth parasites appear to exploit the TGF-β pathway to suppress host immunity.

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TGF-β homologues and mimics from parasites offer a new route for therapeutic tolerance induction.

The TGF-β superfamily is an ancient metazoan protein class which cuts across cell and tissue differentiation, developmental biology and immunology. Its many members are regulated at multiple levels from intricate control of gene transcription, post-translational processing and activation, and signaling through overlapping receptor structures and downstream intracellular messengers. We have been interested in TGF-β homologues firstly as key players in the induction of immunological tolerance, the topic so closely associated with Ray Owen. Secondly, our interests in how parasites may manipulate the immune system of their host has also brought us to study the TGF-β pathway in infections with longlived, essentially tolerogenic, helminth parasites. Finally, within the spectrum of mammalian TGF-β proteins is an exquisitely tightly-regulated gene, anti-Müllerian hormone (AMH), whose role in sex determination underpins the phenotype of freemartin calves that formed the focus of Ray’s seminal work on immunological tolerance.

Differential Effects of Calcineurin and Mammalian Target of Rapamycin Inhibitors on Alloreactive Th1, Th17, and Regulatory T Cells

BACKGROUND

Previously, we had reported the role of tacrolimus (TAC) versus sirolimus (SRL) on the generation of regulatory T cells (Tregs) in primary MLR assays with SRL, demonstrating a uniquely supportive effect. However, the mechanisms associated with their actions on alloreactive human T cells are not fully understood. Therefore, we tested whether TAC and SRL differentially affect already alloactivated human CD4 T-cell subsets.

METHODS

Alloreactive CD4CD45RA/CD45RO T cells generated in 9-day MLR were cocultured with anti-CD3 and autologous antigen presenting cells plus interleukin (IL)-2 in presence of TAC, SRL, or both, and the Tregs generated after another 5 to 6 days were phenotypically, molecularly, and functionally characterized.

RESULTS

Tacrolimus significantly and SRL modestly inhibited interferon (IFN)-γ (Th1) and IL-17 (Th17)-producing cells. At clinical therapeutic concentrations, SRL, however, significantly increased forkhead/winged helix transcription factor P3 (FOXP3) Tregs, whereas TAC inhibited this T-cell population dose dependently and significantly. When used in combination, TAC and SRL had additive effects on inhibition of IFN-γ- and IL-17-producing cells. This was in contrast to the ability of SRL to reverse TAC-mediated inhibition of FOXP3-expressing cells. Proinflammatory cytokines (IL-1β, IL-6, and tumor necrosis factor-α) added to cultures caused significant decrease in FOXP3 Tregs that was again reversed by SRL. Sirolimus-derived Tregs were phenotypically normal, anergic to allostimulation, and suppressed proliferation of allogeneic effector T-cells.

CONCLUSIONS

Thus, although TAC inhibits all alloreactive T cells, SRL promotes the differentiation and expansion of donor-specific Tregs without secondary reprogramming to IFN-γFOXP3 and IL-17FOXP3 Treg subsets. These results, although performed in an artificial in vitro model, add clinically applicable information on how these agents affect T-cell subpopulations.

Sphingosine 1-Phosphate Receptor 3-Deficient Dendritic Cells Modulate Splenic Responses to Ischemia-Reperfusion Injury

The plasticity of dendritic cells (DCs) permits phenotypic modulation ex vivo by gene expression or pharmacologic agents, and these modified DCs can exert therapeutic immunosuppressive effects in vivo through direct interactions with T cells, either inducing T regulatory cells (T(REG)s) or causing anergy. Sphingosine 1-phosphate (S1P) is a sphingolipid and the natural ligand for five G protein-coupled receptors (S1P1, S1P2, S1P3, S1P4, and S1P5), and S1PR agonists reduce kidney ischemia-reperfusion injury (IRI) in mice. S1pr3(-/-)mice are protected from kidney IRI, because DCs do not mature. We tested the therapeutic advantage of S1pr3(-/-) bone marrow-derived dendritic cell (BMDC) transfers in kidney IRI. IRI produced a rise in plasma creatinine (PCr) levels in mice receiving no cells (NCs) and mice pretreated with wild-type (WT) BMDCs. However, S1pr3(-/-) BMDC-pretreated mice were protected from kidney IRI. S1pr3(-/-) BMDC-pretreated mice had significantly higher numbers of splenic T(REG)s compared with NC and WT BMDC-pretreated mice. S1pr3(-/-) BMDCs did not attenuate IRI in splenectomized, Rag-1(-/-), or CD11c(+) DC-depleted mice. Additionally, S1pr3(-/-) BMDC-dependent protection required CD169(+)marginal zone macrophages and the macrophage-derived chemokine CCL22 to increase splenic CD4(+)Foxp3(+) T(REG)s. Pretreatment with S1pr3(-/-) BMDCs also induced T(REG)-dependent protection against IRI in an allogeneic mouse model. In summary, adoptively transferred S1pr3(-/-) BMDCs prevent kidney IRI through interactions within the spleen and expansion of splenic CD4(+)Foxp3(+) T(REG)s. We conclude that genetically induced deficiency of S1pr3 in allogenic BMDCs could serve as a therapeutic approach to prevent IRI-induced AKI.

Immunological profiling of haemodialysis patients and young healthy individuals with implications for clinical regulatory T cell sorting

With the increasing interest in clinical trials with regulatory T cells (Tregs), immunological profiling of prospective target groups and standardized procedures for Treg isolation are needed. In this study, flow cytometry was used to assess peripheral blood lymphocyte profiles of young healthy individuals and patients undergoing haemodialysis treatment. Tregs obtained from the former may be used in haematopoietic stem cell transplantation and Tregs from the latter in the prevention of kidney transplant rejection. FOXP3 mRNA expression with accompanying isoform distribution was also assessed by the quantitative reverse transcriptase polymerase chain reaction. Flow-cytometric gating strategies were systematically analysed to optimize the isolation of Tregs. Our findings showed an overall similar immunological profile of both cohorts in spite of great differences in both age and health. Analysis of flow-cytometric gating techniques highlighted the importance of gating for both CD25high and CD127low expression in the isolation of FOXP3-positive cells. This study provides additional insight into the immunological profile of young healthy individuals and uraemic patients as well as in-depth analysis of flow-cytometric gating strategies for Treg isolation, supporting the development of Treg therapy using cells from healthy donors and uraemic patients.

Emerging roles of regulatory T cells in tumour progression and metastasis

The metastasis of cancer is a complex and life-threatening process that is only partially understood. Immune suppressive cells are recognized as important contributors to tumour progression and may also promote the development and growth of tumour metastases. Specifically, regulatory T cells (Tregs) have been found to promote primary tumour progression, and emerging pre-clinical data suggests that Tregs may promote metastasis and metastatic tumour growth. While the precise role that Tregs play in metastatic progression is understudied, recent findings have indicated that by suppressing innate and adaptive anti-tumour immunity, Tregs may shield tumour cells from immune detection, and thereby allow tumour cells to survive, proliferate and acquire characteristics that facilitate dissemination. This review will highlight our current understanding of Tregs in metastasis, including an overview of pre-clinical findings and discussion of clinical data regarding Tregs and therapeutic outcome. Evolving strategies to directly ablate Tregs or to inhibit their function will also be discussed. Improving our understanding of how Tregs may influence tumour metastasis may lead to novel treatments for metastatic cancer.

A CB2-Selective Cannabinoid Suppresses T-Cell Activities and Increases Tregs and IL-10

We have previously shown that agonists selective for the cannabinoid receptor 2 (CB2), including O-1966, inhibit the Mixed Lymphocyte Reaction (MLR), an in vitro correlate of organ graft rejection, predominantly through effects on T-cells. Current studies explored the mechanism of this immunosuppression by O-1966 using mouse spleen cells. Treatment with O-1966 dose-relatedly decreased levels of the active nuclear forms of the transcription factors NF-κB and NFAT in wild-type T-cells, but not T-cells from CB2 knockout (CB2R k/o) mice. Additionally, a gene expression profile of purified T-cells from MLR cultures generated using a PCR T-cell activation array showed that O-1966 decreased mRNA expression of CD40 ligand and CyclinD3, and increased mRNA expression of Src-like-adaptor 2 (SLA2), Suppressor of Cytokine Signaling 5 (SOCS5), and IL-10. The increase in IL-10 was confirmed by measuring IL-10 protein levels in MLR culture supernatants. Further, an increase in the percentage of regulatory T-cells (Tregs) was observed in MLR cultures. Pretreatment with anti-IL-10 resulted in a partial reversal of the inhibition of proliferation and blocked the increase of Tregs. Additionally, O-1966 treatment caused a dose-related decrease in the expression of CD4 in MLR cultures from wild-type, but not CB2R k/o, mice. These data support the potential of CB2-selective agonists as useful therapeutic agents to prolong graft survival in transplant patients, and strengthens their potential as a new class of immunosuppressive agents with broader applicability.

The potential role for regulatory T-cell therapy in vascularized composite allograft transplantation

PURPOSE OF REVIEW

Vascularized composite allograft (VCA) transplantation restores defects to a degree not possible by conventional techniques. However, it is limited by the need for long-term immunosuppression and high rates of acute rejection directed against skin. There is therefore a need for a therapy that may shift the risk-benefit ratio in favour of VCA transplantation. Regulatory T cells (Tregs) are a subset of T cells with potent immunoregulatory properties and the potential to promote immunosuppression-free allograft survival. In this review, we consider the evidence for Treg therapy in VCA transplantation.

RECENT FINDINGS

CD4 Tregs are the best-studied immunoregulatory cell type, and a large amount of experimental and clinical data is emerging to endorse their use in VCA transplantation. Data from animal and humanized models are particularly encouraging and demonstrate the potent efficacy of Treg at preventing skin allograft rejection. Moreover, central tolerance induction techniques in VCA transplantation models are demonstrating a dependence on Tregs for graft survival.

SUMMARY

An improvement in outcomes after VCA transplantation has the potential to revolutionize the field. Several effective therapeutic strategies have demonstrated great promise experimentally, and there is now a need to assess their safety and efficacy in a clinical setting.

TLR4 regulates IFN-γ and IL-17 production by both thymic and induced Foxp3+ Tregs during intestinal inflammation

Tregs play a crucial role in the maintenance of intestinal immune homeostasis. However, significant numbers of Foxp3(+) Tregs accumulate in the inflamed lesions in experimental colitis and in IBD patients. Treg production of the proinflammatory cytokines IFN-γ and/or IL-17 may arguably explain their ineffectiveness in suppressing intestinal inflammation. However, it remains unknown whether iTreg and tTreg produce proinflammatory cytokines and how TLR signaling regulates this process. Here, we found that Foxp3(+)Tregs were increased in the intestines of B6.TLR4(-/-) and B6.IL-10(-/-) mice when compared with WT B6 mice. TLR4(-/-) and IL-10(-/-) resulted in more Tregs within inflamed intestines. The majority of Foxp3(+) Tregs in the spleen was Helios(+)Nrp1(+), whereas most Foxp3(+) Tregs in the intestinal LP were Helios(-)Nrp1(-). More Helios(+)Nrp1(+) Tregs expressed IFN-γ and/or IL-17 than did Helios(-)Nrp1(-) Tregs in the spleen and intestine, which was increased with TLR4(-/-). TLR4 signaling in T cells and APCs inhibited Foxp3(+) induction via MyD88-dependent, TRIF-independent pathways, which was negatively regulated by SOCS3. Collectively, these data demonstrate Helios(+)Nrp1(+) tTregs and Helios(-)Nrp1(-) iTregs produce proinflammatory cytokines in the intestines during inflammation, which was regulated by TLR4 signaling.

Helminths and immunological tolerance

Current immunosuppression regimens for solid-organ transplantation have shown disappointing efficacy in the prevention of chronic allograft rejection and carry unacceptable risks including toxicity, neoplasia, and life-threatening infection. Achievement of immunological tolerance (long-term antigen unresponsiveness in an immunocompetent host) presents the exciting prospect of freedom from immunosuppression for transplant recipients. It is now 60 years since the first demonstration of immunological tolerance in animal models of transplantation, but translation into routine clinical practice remains elusive. Helminth parasites may provide novel strategies toward achieving this goal. Helminths are remarkably successful parasites: they currently infect more than one quarter of the world’s population. It is now well established that the parasites’ success is the result of active immunomodulation of their hosts’ immune response. Although this primarily secures ongoing survival of the parasites, helminth-induced immunomodulation can also have a number of benefits for the host. Significant reductions in the prevalence of allergy and autoimmune conditions among helminth-infected populations are well recognized and there is now a significant body of evidence to suggest that harmful immune responses to alloantigens may be abrogated as well. Here, we review all existing studies of helminth infection and transplantation, explore the mechanisms involved, and discuss possible avenues for future translation to clinical practice.

Harnessing FOXP3+ regulatory T cells for transplantation tolerance

Early demonstrations that mice could be tolerized to transplanted tissues with short courses of immunosuppressive therapy and that with regard to tolerance to self, CD4+FOXP3+ regulatory T cells (Tregs) appeared to play a critical role, have catalyzed strategies to harness FOXP3-dependent processes to control rejection in human transplantation. This review seeks to examine the scientific underpinning for this new approach to finesse immunosuppression.

Combination peptide immunotherapy suppresses antibody and helper T-cell responses to the RhD protein in HLA-transgenic mice

The offspring from pregnancies of women who have developed anti-D blood group antibodies are at risk of hemolytic disease of the newborn. We have previously mapped four peptides containing immunodominant T-helper cell epitopes from the RhD protein and the purpose of the work was to develop these into a product for suppression of established anti-D responses. A panel of each of the four immunodominant RhD peptides was synthesized with modifications to improve manufacturability and solubility, and screened for retention of recognition by human T-helper cells. A selected version of each sequence was combined in a mixture (RhDPmix), which was tested for suppressive ability in a humanized murine model of established immune responses to RhD protein. After HLA-DR15 transgenic mice had been immunized with RhD protein, a single dose of RhDPmix, given either intranasally (P=0.008, Mann-Whitney rank sum test) or subcutaneously (P=0.043), rapidly and significantly suppressed the ongoing antibody response. This was accompanied by reduced T-helper cell responsiveness, although this change was less marked for subcutaneous RhDPmix delivery, and by the recruitment of cells with a regulatory T-cell phenotype. The results support human trials of RhDPmix peptide immunotherapy in women with established antibody responses to the RhD blood group.

TNF Receptor 2 and Disease: Autoimmunity and Regenerative Medicine

The regulatory cytokine tumor necrosis factor (TNF) exerts its effects through two receptors: TNFR1 and TNFR2. Defects in TNFR2 signaling are evident in a variety of autoimmune diseases. One new treatment strategy for autoimmune disease is selective destruction of autoreactive T cells by administration of TNF, TNF inducers, or TNFR2 agonism. A related strategy is to rely on TNFR2 agonism to induce T-regulatory cells (T_regs) that suppress cytotoxic T cells. Targeting TNFR2 as a treatment strategy is likely superior to TNFR1 because of its more limited cellular distribution on T cells, subsets of neurons, and a few other cell types, whereas TNFR1 is expressed throughout the body. This review focuses on TNFR2 expression, structure, and signaling; TNFR2 signaling in autoimmune disease; treatment strategies targeting TNFR2 in autoimmunity; and the potential for TNFR2 to facilitate end organ regeneration.

Regulatory dendritic cell therapy: from rodents to clinical application

Dendritic cells (DC) are highly-specialized, bone marrow-derived antigen-presenting cells that induce or regulate innate and adaptive immunity. Regulatory or "tolerogenic" DC play a crucial role in maintaining self tolerance in the healthy steady-state. These regulatory innate immune cells subvert naïve or memory T cell responses by various mechanisms. Regulatory DC (DCreg) also exhibit the ability to induce or restore T cell tolerance in many animal models of autoimmune disease or transplant rejection. There is also evidence that adoptive transfer of DCreg can regulate T cell responses in non-human primates and humans. Important insights gained from in vitro studies and animal models have led recently to the development of clinical grade human DCreg, with potential to treat autoimmune disease or enhance transplant survival while reducing patient dependency on immunosuppressive drugs. Phase I trials have been conducted in type-1 diabetes and rheumatoid arthritis, with results that emphasize the feasibility and safety of DCreg therapy. This mini-review will outline how observations made using animal models have been translated into human use, and discuss the challenges faced in further developing this form of regulatory immune cell therapy in the fields of autoimmunity and transplantation.