CD4+CD25+ T Regulatory Cells in Transplantation Tolerance: 25 Years On

T cell activation and deficits in T regulatory cells are associated with major depressive disorder and severity of depression

Major depressive disorder (MDD) is associated with T cell activation, but no studies have examined the combined effects of T cell activation and deficits in T regulatory (Treg) cells on the severity of acute phase MDD. Using flow cytometry, we determined the percentage and median fluorescence intensity of CD69, CD71, CD40L, and HLADR-bearing CD3+, CD4+, and CD8+ cells, and cannabinoid type 1 receptor (CB1), CD152 and GARP (glycoprotein A repetitions predominant)-bearing CD25+ FoxP3 T regulatory (Treg) cells in 30 MDD patients and 20 healthy controls in unstimulated and stimulated (anti-CD3/CD28) conditions. Based on cytokine levels, we assessed M1 macrophage, T helper (Th)-1 cell, immune-inflammatory response system (IRS), T cell growth, and neurotoxicity immune profiles. We found that the immune profiles (including IRS and neurotoxicity) were significantly predicted by decreased numbers of CD152 or GARP-bearing CD25+ FoxP3 cells or CD152 and GARP expression in combination with increases in activated T cells (especially CD8+ CD40L+ percentage and expression). MDD patients showed significantly increased numbers of CD3+ CD71+, CD3+ CD40L+, CD4+ CD71+, CD4+ CD40L+, CD4+ HLADR+, and CD8+ HLADR+ T cells, increased CD3+ CD71+, CD4+ CD71+ and CD4+ HLADR+ expression, and lowered CD25+ FoxP3 expression and CD25+ FoxP+ CB1+ numbers as compared with controls. The Hamilton Depression Rating Scale score was strongly predicted (between 30 and 40% of its variance) by a lower number of CB1 or GARP-bearing Treg cells and one or more activated T cell subtypes (especially CD8+ CD40L+). In conclusion, increased T helper and cytotoxic cell activation along with decreased Treg homeostatic defenses are important parts of MDD that lead to enhanced immune responses and, as a result, neuroimmunotoxicity.

Small-molecule TIP60 inhibitors enhance regulatory T cell induction through TIP60-P300 acetylation crosstalk

Foxp3 acetylation is essential to regulatory T (Treg) cell stability and function, but pharmacologically increasing it remains an unmet challenge. Here, we report that small-molecule compounds that inhibit TIP60, an acetyltransferase known to acetylate Foxp3, unexpectedly increase Foxp3 acetylation and Treg induction. Utilizing a dual experimental/computational approach combined with a newly developed FRET-based methodology compatible with flow cytometry to measure Foxp3 acetylation, we unraveled the mechanism of action of these small-molecule compounds in murine and human Treg induction cell cultures. We demonstrate that at low-mid concentrations they activate TIP60 to acetylate P300, a different acetyltransferase, which in turn increases Foxp3 acetylation, thereby enhancing Treg cell induction. These results reveal a potential therapeutic target relevant to autoimmunity and transplant.

Effectiveness of Expressive Writing in Kidney Transplanted Patients: A Randomized Controlled Trial Study

The present study aimed to assess the effectiveness of an expressive writing (EW) intervention on psychological and physiological variables after kidney transplant. The final sample of 26 were randomly assigned to an expressive writing group (EWG) and control group (CG). Outcomes were focused on depression, anxiety, alexithymia, empathy, resilience, locus of control, creatinine, CDK-EPI, and azotemia. Depressive symptoms and alexithymia levels decreased in the EWG, with better adherence. Resilience declined over time in both groups. The EWG showed a significantly higher CDK-EPI, indicating better renal functioning. EW seems an effective intervention to improve the psychological health of transplanted patients, with a possible effect on renal functioning. These findings open the possibility of planning brief psychological interventions aimed at processing emotional involvement, in order to increase adherence, the acceptance of the organ, and savings in healthcare costs.

TFNR2 in Ischemia-Reperfusion Injury, Rejection, and Tolerance in Transplantation

Tumor necrosis factor receptor 2 (TNFR2) has been shown to play a crucial role in CD4+ T regulatory cells (CD4+Tregs) expansion and suppressive function. Increasing evidence has also demonstrated its role in a variety of immune regulatory cell subtypes such as CD8+ T regulatory cells (CD8+ Tregs), B regulatory cells (Bregs), and myeloid-derived suppressor cells (MDSCs). In solid organ transplantation, regulatory immune cells have been associated with decreased ischemia-reperfusion injury (IRI), improved graft survival, and improved overall outcomes. However, despite TNFR2 being studied in the context of autoimmune diseases, cancer, and hematopoietic stem cell transplantation, there remains paucity of data in the context of solid organ transplantation and islet cell transplantation. Interestingly, TNFR2 signaling has found a clinical application in islet transplantation which could guide its wider use. This article reviews the current literature on TNFR2 expression in immune modulatory cells as well as IRI, cell, and solid organ transplantation. Our results highlighted the positive impact of TNFR2 signaling especially in kidney and islet transplantation. However, further investigation of TNFR2 in all types of solid organ transplantation are required as well as dedicated studies on its therapeutic use during induction therapy or treatment of rejection.

Interferon-β acts directly on T cells to prolong allograft survival by enhancing regulatory T cell induction through Foxp3 acetylation

Type I interferons (IFNs) are pleiotropic cytokines with potent antiviral properties that also promote protective T cell and humoral immunity. Paradoxically, type I IFNs, including the widely expressed IFNβ, also have immunosuppressive properties, including promoting persistent viral infections and treating T-cell-driven, remitting-relapsing multiple sclerosis. Although associative evidence suggests that IFNβ mediates these immunosuppressive effects by impacting regulatory T (Treg) cells, mechanistic links remain elusive. Here, we found that IFNβ enhanced graft survival in a Treg-cell-dependent murine transplant model. Genetic conditional deletion models revealed that the extended allograft survival was Treg cell-mediated and required IFNβ signaling on T cells. Using an in silico computational model and analysis of human immune cells, we found that IFNβ directly promoted Treg cell induction via STAT1- and P300-dependent Foxp3 acetylation. These findings identify a mechanistic connection between the immunosuppressive effects of IFNβ and Treg cells, with therapeutic implications for transplantation, autoimmunity, and malignancy.

Interleukin-5 (IL-5) Therapy Prevents Allograft Rejection by Promoting CD4+CD25+ Ts2 Regulatory Cells That Are Antigen-Specific and Express IL-5 Receptor

CD4⁺CD25⁺Foxp3⁺T cell population is heterogenous and contains three major sub-groups. First, thymus derived T regulatory cells (tTreg) that are naïve/resting. Second, activated/memory Treg that are produced by activation of tTreg by antigen and cytokines. Third, effector lineage CD4⁺CD25⁺T cells generated from CD4⁺CD25^- T cells' activation by antigen to transiently express CD25 and Foxp3. We have shown that freshly isolated CD4⁺CD25⁺T cells are activated by specific alloantigen and IL-4, not IL-2, to Ts2 cells that express the IL-5 receptor alpha. Ts2 cells are more potent than naïve/resting tTreg in suppressing specific alloimmunity. Here, we showed rIL-5 promoted further activation of Ts2 cells to Th2-like Treg, that expressed foxp3, irf4, gata3 and il5. In vivo, we studied the effects of rIL-5 treatment on Lewis heart allograft survival in F344 rats. Host CD4⁺CD25⁺T cells were assessed by FACS, in mixed lymphocyte culture and by RT-PCR to examine mRNA of Ts2 or Th2-like Treg markers. rIL-5 treatment given 7 days after transplantation reduced the severity of rejection and all grafts survived ≥60d whereas sham treated rats fully rejected by day 31 (p<0.01). Treatment with anti-CD25 or anti-IL-4 monoclonal antibody abolished the benefits of treatment with rIL-5 and accelerated rejection. After 10d treatment with rIL-5, hosts' CD4⁺CD25⁺ cells expressed more Il5ra and responded to specific donor Lewis but not self. Enriched CD4⁺CD25⁺ cells from rIL-5 treated rats with allografts surviving >60 days proliferated to specific donor only when rIL-5 was present and did not proliferate to self or third party. These cells had more mRNA for molecules expressed by Th2-like Treg including Irf4, gata3 and Il5. These findings were consistent with IL-5 treatment preventing rejection by activation of Ts2 cells and Th2-like Treg.

Flow cytometric analysis of T lymphocytes and cytokines in aqueous humor of patients with varicella zoster virus-mediated acute retinal necrosis

BACKGROUND

The purpose of this study is to investigate the aqueous humor (AH) T lymphocyte subsets and cytokines of acute retinal necrosis (ARN) to elucidate the immunologic inflammatory features of this disorder.

METHODS

Three patients with ARN infected with varicella zoster virus (VZV) who underwent multiple intravitreal injections of ganciclovir were enrolled in this study. The control group consisted of four non-infectious patients with acute anterior uveitis (AAU). Flow cytometric analysis was performed on the lymphocyte subsets from the AH and peripheral blood (PB) samples during the active phase of intraocular inflammation. Five inflammatory cytokines were measured in each AH sample and various clinical characteristics were also assessed.

RESULTS

VZV deoxyribonucleic acid (DNA) was detected by real-time polymerase chain reaction (PCR) in AH from all the ARN patients, who showed higher CD8+ T lymphocytes population in AH than the AAU patients (p = 0.006). CD4/CD8 ratios of T lymphocytes and the percentage of CD8 + CD25+ T lymphocytes in AH were significantly lower in ARN than in AAU (p = 0.006; p = 0.012). In the ARN patients, the percentages of CD4+ and CD8+ T lymphocytes in AH were higher than those found in PB. The percentage of CD4 + CD25+ T lymphocytes in AH was significantly higher than the proportion in PB in the AAU patients (p = 0.001). Immunoregulatory cytokine Interleukin-10 in AH was significantly elevated in the ARN patients in comparison with the case of the AAU patients (p = 0.036). In ARN, the copy number of VZV DNA in AH positively correlated with the percentage of CD8+ T lymphocytes in AH and negatively correlated with the CD4/CD8 ratio in AH during the course of disease treatment (p = 0.009, r = 0.92; p = 0.039, r = - 0.834).

CONCLUSION

The ARN patients caused by VZV had different intraocular T lymphocyte subsets and cytokines profile than those of the non-infectious patients. High percentages of CD8+ T lymphocytes and low CD4/CD8 T cell ratios may be a potential biomarker for diagnosis of viral-infectious uveitis. T lymphocytes examination at the inflammatory sites has the potential to become a useful research tool for differentiating viral and non-viral uveitis.

The Role of Regulatory Myeloid Cell Therapy in Renal Allograft Rejection

Kidney transplantation is a primary therapy for end-stage renal disease (ESRD) all the time. But it does not mean that we have fully unraveling the mystery of kidney transplantation and confer every patient favorable prognosis. Immune rejection has always been a stumbling block when we try to increase the success rate of kidney transplantation and improve long-term outcomes. Even if the immune rejection is effectively controlled in acute phase, there is a high possibility that the immune response mediated by chronically activated antibodies will trigger chronic rejection and ultimately lead to graft failure. At present, immunosuppressive agent prepared chemically is mainly used to prevent acute or chronic rejection, but it failed to increase the long-term survival rate of allografts or reduce the incidence of chronic rejection after acute rejection, and is accompanied by many adverse reactions. Therefore, many studies have begun to use immune cells to regulate the immune response in order to control allograft rejection. This article will focus on the latest study and prospects of more popular regulatory myeloid cells in the direction of renal transplantation immunotherapy and introduce their respective progress from experimental research to clinical research.

PD-L1 cellular nanovesicles carrying rapamycin inhibit alloimmune responses in transplantation

Organ transplantation has been employed upon serious injuries, but a T-cell-mediated potent inflammatory immune response often leads to graft rejection. Immunosuppressive drugs such as rapamycin (RAPA) have to be taken after organ transplantation, but long-term use of these drugs causes severe adverse effects. Immune checkpoint pathways such as the programmed death-receptor 1/programmed death-ligand 1 (PD-1/PD-L1) provides an immunosuppressive environment, preventing excessive tissue destruction due to inflammatory immune responses. In this study, we bioengineered cell membrane-derived PD-L1 nanovesicles (PD-L1 NVs) to carry low doses of RAPA. These NVs inhibited T-cell activation and proliferation in vitro, by enhancing the PD-1/PD-L1 immune co-inhibitory signaling axis and inhibiting the mTOR pathway. Importantly, PD-L1 NVs encapsulated with rapamycin exerted stronger effects on inhibiting T-cell proliferation than PD-L1 NVs or rapamycin alone. This can be recapitulated in a mouse skin transplantation model, leading to the weakened alloimmune response and allograft tolerance. We also found that PD-L1/rapamycin vesicles have additional function to induce regulatory T cells in the recipient spleens. Our study highlighted the power of combining low-dose rapamycin and PD-L1 in the nanovesicles as immunosuppressants to promote allograft acceptance.

B-Cell Control of Regulatory T Cells in Friend Virus Infection

B lymphocytes have well-established effector roles during viral infections, including production of antibodies and functioning as antigen-presenting cells for CD4+ and CD8+ T cells. B cells have also been shown to regulate immune responses and induce regulatory T cells (Tregs). In the Friend virus (FV) model, Tregs are known to inhibit effector CD8+ T-cell responses and contribute to virus persistence. Recent work has uncovered a role for B cells in the induction and activation of Tregs during FV infection. In addition to inducing Tregs, B cell antibody production and antigen-presenting cell activity is a target of Treg suppression. This review focuses on the dynamic interactions between B cells and Tregs during FV infection.

Tolerogenic vaccines: Targeting the antigenic and cytokine niches of FOXP3+ regulatory T cells

FOXP3+ regulatory T cells (Tregs) constitute a critical barrier that enforces tolerance to both the self-peptidome and the extended-self peptidome to ensure tissue-specific resistance to autoimmune, allergic, and other inflammatory disorders. Here, we review intuitive models regarding how T cell antigen receptor (TCR) specificity and antigen recognition efficiency shape the Treg and conventional T cell (Tcon) repertoires to adaptively regulate T cell maintenance, tissue-residency, phenotypic stability, and immune function in peripheral tissues. Three zones of TCR recognition efficiency are considered, including Tcon recognition of specific low-efficiency self MHC-ligands, Treg recognition of intermediate-efficiency agonistic self MHC-ligands, and Tcon recognition of cross-reactive high-efficiency agonistic foreign MHC-ligands. These respective zones of TCR recognition efficiency are key to understanding how tissue-resident immune networks integrate the antigenic complexity of local environments to provide adaptive decisions setting the balance of suppressive and immunogenic responses. Importantly, deficiencies in the Treg repertoire appear to be an important cause of chronic inflammatory disease. Deficiencies may include global deficiencies in Treg numbers or function, subtle 'holes in the Treg repertoire' in tissue-resident Treg populations, or simply Treg insufficiencies that are unable to counter an overwhelming molecular mimicry stimulus. Tolerogenic vaccination and Treg-based immunotherapy are two therapeutic modalities meant to restore dominance of Treg networks to reverse chronic inflammatory disease. Studies of these therapeutic modalities in a preclinical setting have provided insight into the Treg niche, including the concept that intermediate-efficiency TCR signaling, high IFN-β concentrations, and low IL-2 concentrations favor Treg responses and active dominant mechanisms of immune tolerance. Overall, the purpose here is to assimilate new and established concepts regarding how cognate TCR specificity of the Treg repertoire and the contingent cytokine networks provide a foundation for understanding Treg suppressive strategy.

Therapeutic Effects of Anti-Bone Morphogenetic Protein and Activin Membrane-Bound Inhibitor Treatment in Psoriasis and Arthritis

OBJECTIVE

The transforming growth factor β (TGFβ) inhibitor BAMBI (bone morphogenetic protein and activin membrane-bound inhibitor) has been shown to control differentiation of CD4+ T lymphocytes into either tolerogenic Treg cells or pathogenic Th17 cells, through the regulation of TGFβ and interleukin-2 (IL-2) signaling strength. The present study was undertaken to explore the potential beneficial effects of this strategy of pharmacologic inhibition using novel anti-BAMBI monoclonal antibodies (mAb) in different experimental murine models of chronic skin and joint inflammatory/autoimmune disease.

METHODS

Development of Saccharomyces cerevisiae mannan-induced psoriatic arthritis (MIP) (n = 18-30 mice per group), imiquimod-induced skin psoriasis (n = 20-30 mice per group), or type II collagen-induced arthritis (CIA) (n = 13-16 mice per group) was analyzed in a total of 2-5 different experiments with either wild-type (WT) or BAMBI-deficient B10.RIII mice that were left untreated or treated with mAb B101.37 (mouse IgG1 anti-BAMBI), a mouse IgG1 anti-TNP isotype control, anti-CD25, or anti-TGFβ mAb.

RESULTS

Treatment of normal mice with IgG1 anti-BAMBI mAb clone B101.37 led to expansion of Treg cells in vivo, and had both preventive and therapeutic effects in mice with MIP (each P < 0.05 versus controls). The conferred protection against disease progression was found to be mediated by Treg cells, which controlled the activation and expansion of pathogenic IL-17-producing cells, and was dependent on the level of TGFβ activity. Furthermore, treatment with B101.37 mAb blocked both the development of skin psoriasis induced by imiquimod and the development of CIA in mice (each P < 0.05 versus controls). Finally, pharmacologic inhibition of BAMBI with the IgM anti-BAMBI mAb B143.14 also potentiated the suppressive activity of Treg cells in vitro (P < 0.001 versus controls).

CONCLUSION

These results in murine models identify BAMBI as a promising new therapeutic target for chronic inflammatory diseases and other pathologic conditions modulated by Treg cells.

Engineering Programmed Death Ligand-1/Cytotoxic T-Lymphocyte-Associated Antigen-4 Dual-Targeting Nanovesicles for Immunosuppressive Therapy in Transplantation

T cell activation by immune allorecognition is a major contributing factor toward the triggering of organ rejection. Immunosuppressive drugs have to be taken after organ transplantation, but long-term use of these drugs increases the risks of infection and other serious disorders. Here, we showed dysregulation of programmed cell death-ligand 1/programmed cell death 1 (PD-L1/PD-1) and cytotoxic T-lymphocyte-associated protein 4/cluster of differentiation 80 (CTLA-4/CD80) in the spleen of two organ transplantation models. Using a bioengineering approach, cellular exosome-like nanovesicles (NVs) displaying PD-L1/CTLA-4 dual-targeting cargos were designed, and their specificity to bind their ligands PD-1 and CD80 on T cell and dendritic cell surfaces was confirmed. These NVs consequently enhanced PD-L1/PD-1 and CTLA-4/CD80 immune inhibitory pathways, two key immune checkpoints to co-inhibit T cell activation and maintain peripheral tolerance. It was also confirmed that PD-L1/CTLA-4 NVs led to the reduction of T cell activation and proliferation in vitro and in vivo. Finally, it was demonstrated that PD-L1/CTLA-4 NVs reduced density of CD8⁺ T cells and cytokine production, enriched regulatory T cells, and prolonged the survival of mouse skin and heart grafts. Taken together, these data supported the idea that PD-L1/CTLA-4 dual-targeting NVs exert immune inhibitory effects and may be used as a prospective immunosuppressant in organ transplantation.

Chimerism, Transplant Tolerance, and Beyond

The present review discusses current developments in tolerance induction for solid organ transplantation with a particular emphasis on chimerism-based approaches. It explains the basic mechanisms of chimerism-based tolerance and provides an update on ongoing clinical tolerance trials. The concept of "delayed tolerance" is presented, and ongoing preclinical studies in the nonhuman primate setting-including current limitations and hurdles regarding this approach-are illustrated. In addition, a brief overview and update on cell-based tolerogenic clinical trials is provided. In a critical approach, advantages, limitations, and potential implications for the future of these different regimens are discussed.

Toll-Like Receptor 3 Activator Preconditioning Enhances Modulatory Function of Adipose‑Derived Mesenchymal Stem Cells in a Fully MHC-Mismatched Murine Model of Heterotopic Heart Transplantation

Background

Donor-specific tolerance is the ultimate goal in organ transplantation. Diverse approaches, including the use of mesenchymal stem cells (MSCs), have been investigated to induce graft tolerance. Non-stimulated MSCs showed limited regulatory functions through interaction with multiple immune-regulatory cells, such as regulatory T cells (Tregs). To augment their functions, MSCs have been preconditioned with toll-like receptor (TLR3/4) agonist in autoimmune disease models, but results were conflicting.

Material/Methods

We evaluated the immunomodulatory effects of mouse adipose-derived mesenchymal stem cells (ADSCs) preconditioned with various combinations of TLR3/4 agonist and antagonists, including polyinosinic-polycytidylic acid poly(I:C)-TLR3 agonist, lipopolysaccharide (LPS) -TLR4 agonist, and TAK242-TLR4 antagonist. In vitro and in vivo experiments including mixed lymphocyte reaction, cytokines measurement, Tregs analysis, and a fully mismatched MHC heterotopic heart transplantation in mice (BALB/c to C57BL/6) were conducted.

Results

ADSCs preconditioned with poly(I:C) showed the highest efficiency in inhibiting lymphocyte proliferation, which was correlated with the upregulation of fibrinogen-like protein 2 (FGL2), an effector molecule of Tregs. The mean survival of cardiac allografts was extended from 8 to 12 days by intravenous injection of a single dose of ADSCs preconditioned with TLR3 agonist. The proportion of Tregs in the recipient’s spleen was significantly increased by injecting the poly(I:C)-stimulated ADSCs.

Conclusions

These results show that short-term TLR3 agonist preconditioning enhances the immunomodulatory efficacy of ADSCs, which can induce the generation of Tregs and upregulate the expression of FGL2, thereby improving the outcome of patients receiving organ transplantation.

Autoantigen specific IL-2 activated CD4+CD25+T regulatory cells inhibit induction of experimental autoimmune neuritis

Experimental autoimmune neuritis (EAN) induced by peripheral nerve myelin (PNM) is self-limiting and re-immunization with PNM does not re-activate disease. This study showed inhibition of EAN by CD4⁺CD25⁺T cells both from sensitized hosts or from naïve hosts after ex-vivo activation by PNM and rIL-2. Transfer of naïve CD4⁺CD25⁺T cells has no effect on EAN, nor did naïve CD4⁺CD25⁺T cells activated with rIL-2 and renal tubular antigen. Culture of naive CD4⁺CD25⁺Treg with rIL-2 and PNM induced mRNA for the IFN-gamma receptor. We showed naïve CD4⁺CD25⁺T cells activated by specific auto-antigen and rIL-2 produced more potent antigen-specific Treg that may have therapeutic potential.

A case for the reuse and adaptation of mechanistic computational models to study transplant immunology

Computational mechanistic models constitute powerful tools for summarizing our knowledge in quantitative terms, providing mechanistic understanding, and generating new hypotheses. The present review emphasizes the advantages of reusing publicly available computational models as a way to capitalize on existing knowledge, reduce the number of parameters that need to be adjusted to experimental data, and facilitate hypothesis generation. Finally, it includes a step-by-step example of the reuse and adaptation of an existing model of immune responses to tuberculosis, tumor growth, and blood pathogens, to study donor-specific antibody (DSA) responses. This review aims to illustrate the benefit of leveraging the currently available computational models in immunology to accelerate the study of alloimmune responses, and to encourage modelers to share their models to further advance our understanding of transplant immunology.

Increased frequency of CD4+ CD25high CD127low T cells early after lung transplant is associated with improved graft survival - a retrospective study

In this retrospective study, we analyzed the presence of any association of three CD4⁺ CD25^high regulatory T-cell subpopulations at 3 weeks after lung transplantation with the later incidence of chronic lung allograft dysfunction and graft survival. Among lung-transplanted patients between January 2009 and April 2018, only patients with sufficient T-cell measurements at 3 weeks after transplantation were included into the study. Putative regulatory T cells were defined as CD4⁺ CD25^high T cells, detected in peripheral blood and further analyzed for CD127^low , FoxP3⁺ , and CD152⁺ using fluorescence-activated cell sorting (FACS) analysis. Associations of regulatory T cells with chronic lung allograft dysfunction (CLAD) and graft survival were evaluated using Cox analysis. During the study period, 724 (71%) patients were included into the study. Freedom from chronic lung allograft dysfunction (CLAD) and graft survival amounted to 66% and 68% at 5 years. At the multivariable analysis, increasing frequencies of CD127^low were associated with better freedom from CLAD (hazard ratio for each 1% increase of %CD127^low , HR = 0.989, 95% CI = 0.981-0.996, P = 0.003) and better graft survival (HR = 0.991, 95% CI = 0.984-0.999, P = 0.026). A higher frequency of CD127^low regulatory T cells in peripheral blood early after lung transplantation estimated a protective effect against chronic lung allograft dysfunction, mortality, and re-transplantation.

Alloactivation of Naïve CD4+CD8-CD25+T Regulatory Cells: Expression of CD8α Identifies Potent Suppressor Cells That Can Promote Transplant Tolerance Induction

Therapy with alloantigen-specific CD4⁺CD25⁺ T regulatory cells (Treg) for induction of transplant tolerance is desirable, as naïve thymic Treg (tTreg) are not alloantigen-specific and are weak suppressor cells. Naïve tTreg from DA rats cultured with fully allogeneic PVG stimulator cells in the presence of rIL-2 express IFN-gamma receptor (IFNGR) and IL-12 receptor beta2 (IL-12Rβ2) and are more potent alloantigen-specific regulators that we call Ts1 cells. This study examined additional markers that could identify the activated alloantigen-specific Treg as a subpopulation within the CD4⁺CD25⁺Foxp3⁺Treg. After culture of naïve DA CD4⁺CD8⁻CD25⁺T cells with rIL-2 and PVG alloantigen, or rIL-2 without alloantigen, CD8α was expressed on 10–20% and CD8β on <5% of these cells. These cells expressed ifngr and Il12rb2. CD8α⁺ cells had increased Ifngr that characterizes Ts1 cells as well was Irf4, a transcription factor induced by TCR activation. Proliferation induced by re-culture with rIL-12 and alloantigen was greater with CD4⁺CD8α⁺CD25⁺Treg consistent with the CD8α⁺ cells expressing IL-12R. In MLC, the CD8α⁺ fraction suppressed responses against allogeneic stimulators more than the mixed Ts1 population, whereas the CD4⁺CD8⁻CD25⁺T cells were less potent. In an adoptive transfer assay, rIL-2 and alloantigen activated Treg suppress rejection at a ratio of 1:10 with naïve effector cells, whereas alloantigen and rIL-2 activated tTreg depleted of the CD8α⁺ cells were much less effective. This study demonstrated that expression of CD8α by rIL-2 and alloantigen activation of CD4⁺CD8⁻CD25⁺Foxp3⁺T cells was a marker of activated and potent Treg that included alloantigen-specific Treg.

Immunophenotyping of Human Regulatory T Cells

Regulatory T cells, also known as Tregs, play a pivotal role in maintaining homeostasis of the immune system and self-tolerance. Tregs express CD3, CD4, CD25, and FOXP3 but lack CD127. CD4 and CD3 identify helper T lymphocytes, of which Tregs are a subset. CD25 is IL-2Rα, an essential activation marker that is expressed in high levels on Tregs. FOXP3 is the canonical transcription factor, important in the development, maintenance, and identification of Tregs. CD127 is IL-7 receptor, expressed inversely with suppression, and is therefore downregulated on Tregs. Flow cytometry is a powerful tool that is capable of simultaneously measuring Tregs along with several markers associated with subpopulations of Tregs, activation, maturation, proliferation, and surrogates of functional suppression. This chapter describes a multicolor flow cytometry-based approach to measure human Tregs, including details for surface staining, fixation/permeabilization, intracellular/intranuclear staining, acquisition of samples on a flow cytometer, plus analysis and interpretation of resulting FCS files.

Mesenchymal stromal cells in kidney transplantation

PURPOSE OF REVIEW

Mesenchymal stromal cells (MSC) have emerged as one of the most promising candidates for immunomodulatory cell therapy in kidney transplantation. Here we describe novel insights into the MSC mechanism of action and provide an overview of initial safety and feasibility studies with MSC in kidney transplantation.

RECENT FINDINGS

Clinical studies of MSC-based cell therapy in kidney transplant recipients demonstrated the safety and feasibility of cell therapy and provide the first encouraging evidence of the efficacy of MSC in enabling the minimization of immunosuppressive drugs. In our initial experience with MSC-based therapy in kidney transplant recipients we carried out extensive clinical and immunological monitoring of MSC-treated patients and found possible biomarkers of MSC immunomodulation in some of them. Based on these biomarkers we identified a patient in whom complete discontinuation of immunosuppression has been achieved safely and successfully.

SUMMARY

Many issues should be addressed before MSC-based therapy becomes a standard treatment protocol for kidney transplantation. A better understanding of the MSC mechanism of action and the identification of biomarkers of response to therapy will inform the rational design of the most effective clinical protocol and the selection of patients amenable to safe immunosuppressive drug withdrawal.

Foxp3+ Regulatory and Conventional CD4+ T Cells Display Similarly High Frequencies of Alloantigen-Reactive Cells

Foxp3⁺ regulatory T cells (Tregs) play a major role in acquired immune tolerance to allogenic transplants. Their suppressive activity is thought to require T cell receptor (TCR)-driven antigen recognition; little, however, is known about the fraction of Tregs able to recognize alloantigens within this T cell subset primarily educated against self-antigens. Performing transfer experiments of Tregs or conventional T cells (Tconv) into both lymphoreplete and lymphopenic mice, we observed a similarly high proportion of cells signaling through their TCR and proliferating in allogenic hosts. Furthermore, using an in vivo proliferation assay with limited T cell numbers infused into lymphopenic mice, we found that the overall frequency of alloreactive Tregs was similar if not higher to that of alloreactive Tconv. Overall our study highlights a noticeably high level of alloreactive Foxp3⁺ regulatory T cells accounting for their predominant role in transplantation tolerance.

Guiding regulatory T cells to the allograft

PURPOSE OF REVIEW

The application of regulatory T cell (Treg) therapy in organ transplantation is actively being pursued using unmodified, typically polyclonal cells. As the results of these ongoing clinical trials emerge, it is time to plan the next wave of clinical trials of Tregs. Here we will review a key strategy to improve Treg effectiveness and reduce side effects, namely increasing Treg specificity - both in terms of antigen recognition and localization to the allograft.

RECENT FINDINGS

Study of chemokine signatures accompanying acute rejection has revealed several chemokines that could be targeted to increase Treg homing. For example, Tregs possessing a Th1-like phenotype and expressing CXCR3 are better able to migrate towards local inflammation. Allografts themselves can be modified to increase Treg-attracting chemokines and Tregs themselves can produce chemokines, facilitating local proximity to their targets of suppression. Finally, tailoring Treg antigen specificity by T-cell or chimeric antigen receptor engineering is another approach to increase the specificity of suppression and optimize localization.

SUMMARY

Treg localization to the graft is important, but the important role of lymph node and germinal center homing cannot be overlooked. There is an opportunity to learn from advances made in cancer immunotherapy to optimize Treg therapy for transplantation.

Role of regulatory T cells in CD47/donor-specific transfusion-induced immune tolerance in skin-heart transplantation mice

OBJECTIVES

To explore the role of regulatory T (T_reg ) cells in the establishment of immune tolerance induced by donor-specific transfusion (DST) in mice with skin-heart transplantation.

METHODS

C57BL/6 mice received DST of splenocytes from CD47^+/+ or CD47^-/- H-2^bm1 mice or no DST 7 days before skin-heart transplantation from major histocompatibility complex class I-mismatched H-2^bm1 donors. The number and proportion of T_reg cells in graft and lymphoid organs were measured by flow cytometry (FACS) and immunohistochemistry (IHC). The inhibitory function of T_reg cells and anti-donor T-cell responses were assessed by mixed lymphocyte reaction.

RESULTS

We observed that mean survival time (MST) of skin or heart graft was significantly longer in C57BL/6 mice which received DST from CD47^+/+ H-2^bm1 mice than from CD47^-/- H-2^bm1 mice. By FACS, we found that the number of T_reg cells in spleen was increased significantly in mice which received CD47^-/- DST compared to mice which received CD47^+/+ DST. However, the percentages of T_reg cells in total splenocytes and lymph node cells were significantly higher in mice that received CD47^+/+ DST than mice which received CD47^-/- DST. Immunohistochemistry showed an increased heart grafts infiltration of T_reg cells in the recipients with CD47^-/- DST, but not CD47^+/+ DST. Supporting this, we found that donor T-cell proliferation was significantly suppressed in mice which received CD47^+/+ DST compared to mice which received CD47^-/- DST. There was no difference of inhibitory function of T_reg cells between these two groups.

CONCLUSION

Our results indicated that CD47 expression on DST cells plays an important role in the induction of immune tolerance in mice with skin-heart transplantation. Increased percentage of T_reg cells may contribute to immune tolerance induced by CD47^+/+ DST.

Dosing optimization of CCR4 immunotoxin for improved depletion of CCR4+ Treg in nonhuman primates

Recently, we have developed a diphtheria toxin‐based recombinant anti‐human CCR4 immunotoxin for targeting CCR4⁺ tumors and Tregs. In this study, we further optimized the dosing schedule for improved CCR4⁺ Treg depletion. We have demonstrated that up to a 90% depletion was achieved and the depletion extended to approximately 2 weeks in the peripheral blood and more than 48 days in the lymph node at 25 μg·kg⁻¹, BID for 8 consecutive days in cynomolgus monkeys. Expansion was observed including monocytes and NK cells. Antibody against the CCR4 immunotoxin was detected after approximately 2 weeks, affecting further depletion efficacy for multiple course treatment.

Interleukin-5 Mediates Parasite-Induced Protection against Experimental Autoimmune Encephalomyelitis: Association with Induction of Antigen-Specific CD4+CD25+ T Regulatory Cells

Objective

To examine if the protective effect of parasite infection on experimental autoimmune encephalomyelitis (EAE) was due to interleukin (IL)-5, a cytokine produced by a type-2 response that induces eosinophilia. We hypothesize that, in parasite infections, IL-5 also promotes expansion of antigen-specific T regulatory cells that control autoimmunity.

Methods

Nippostrongylus brasiliensis larvae were used to infect Lewis rats prior to induction of EAE by myelin basic protein. Animals were sham treated, or given blocking monoclonal antibodies to interleukin 4 or 5 or to deplete CD25⁺ T cells. Reactivity of CD4⁺CD25⁺ T regulatory cells from these animals was examined.

Results

Parasite-infected hosts had reduced severity and length of EAE. The beneficial effect of parasitic infection was abolished with an anti-IL-5 or an anti-CD25 monoclonal antibody (mAb), but not anti-IL-4 mAb. Parasite-infected animals with EAE developed antigen-specific CD4⁺CD25⁺ T regulatory cells earlier than EAE controls and these expressed more Il5ra than controls. Treatment with IL-5 also reduced the severity of EAE and induced Il5ra expressing CD4⁺CD25⁺ T regulatory cells.

Interpretation

The results of this study suggested that IL-5 produced by the type-2 inflammatory response to parasite infection promoted induction of autoantigen-specific CD25⁺Il5ra⁺ T regulatory cells that reduced the severity of autoimmunity. Such a mechanism may explain the protective effect of parasite infection in patients with multiple sclerosis where eosinophilia is induced by IL-5, produced by the immune response to parasites.

In Vivo Attenuation of Antibody-Mediated Acute Renal Allograft Rejection by Ex Vivo TGF-β-Induced CD4+Foxp3+ Regulatory T Cells

Antibody-mediated rejection (AMR) has emerged as the major cause of renal allograft dysfunction, and more effective strategies need to be explored for improving transplant outcomes. Regulatory T cells (Tregs), consisting of at least natural and induced Treg subsets, suppress effector responses at multiple levels and play a key role in transplantation tolerance. In this study, we investigated the effect of induced Tregs (iTregs) on preventing antibody-mediated renal injury and rejection in a mouse model. We observed that infusion of iTregs markedly attenuated histological graft injury and rejection and significantly improved renal allograft survival. iTregs exhibited a comprehensive ability to regulate immunological disorders in AMR. First, iTreg treatment decreased the levels of circulating antidonor antibody and the antibody deposition within allografts. Second, iTregs significantly reduced cell infiltration including CD4⁺ T cells (including Th1, Th17, and Tfh), CD8⁺IFN-γ⁺ cells, natural killer cells, B cells, and plasma cells, which are involved in the process of AMR. Our results also highlight a predominance of M1 macrophage infiltration in grafts with acute AMR, and M1 macrophage could be reduced by iTreg treatment. Collectively, our data demonstrate, for the first time, that TGF-β-induced Tregs can attenuate antibody-mediated acute renal allograft injury through targeting multiple effectors. Thus, use of iTregs in prevention of AMR in clinical practice could be expected.

Cytokines affecting CD4+T regulatory cells in transplant tolerance. III. Interleukin-5 (IL-5) promotes survival of alloantigen-specific CD4+ T regulatory cells

CD4⁺T cells mediate antigen-specific allograft tolerance, but die in culture without activated lymphocyte derived cytokines. Supplementation of the media with cytokine rich supernatant, from ConA activated spleen cells, preserves the capacity of tolerant cells to transfer tolerance and suppress rejection. rIL-2 or rIL-4 alone are insufficient to maintain these cells, however. We observed that activation of naïve CD4⁺CD25⁺FOXP3⁺Treg with alloantigen and the Th2 cytokine rIL-4 induces them to express interleukin-5 specific receptor alpha (IL-5Rα) suggesting that IL-5, a Th2 cytokine that is produced later in the immune response may promote tolerance mediating Treg. This study examined if recombinant IL-5(rIL-5) promoted survival of tolerant CD4⁺, especially CD4⁺CD25⁺T cells. CD4⁺T cells, from DA rats tolerant to fully allogeneic PVG heart allografts surviving over 100days without on-going immunosuppression, were cultured with PVG alloantigen and rIL-5. The ability of these cells to adoptively transfer tolerance to specific-donor allograft and suppress normal CD4⁺T cell mediated rejection in adoptive DA hosts was examined. Tolerant CD4⁺CD25⁺T cells' response to rIL-5 and expression of IL-5Rα was also assessed. rIL-5 was sufficient to promote transplant tolerance mediating CD4⁺T cells' survival in culture with specific-donor alloantigen. Tolerant CD4⁺T cells cultured with rIL-5 retained the capacity to transfer alloantigen-specific tolerance and inhibited naïve CD4⁺T cells' capacity to effect specific-donor graft rejection. rIL-5 promoted tolerant CD4⁺CD25⁺T cells' proliferation in vitro when stimulated with specific-donor but not third-party stimulator cells. Tolerant CD4⁺CD25⁺T cells expressed IL-5Rα. This study demonstrated that IL-5 promoted the survival of alloantigen-specific CD4⁺CD25⁺T cells that mediate transplant tolerance.

Cytokines affecting CD4+T regulatory cells in transplant tolerance. II. Interferon gamma (IFN-γ) promotes survival of alloantigen-specific CD4+T regulatory cells

CD4+T cells that transfer alloantigen-specific transplant tolerance are short lived in culture unless stimulated with specific-donor alloantigen and lymphocyte derived cytokines. Here, we examined if IFN-γ maintained survival of tolerance transferring CD4+T cells. Alloantigen-specific transplant tolerance was induced in DA rats with heterotopic adult PVG heart allografts by a short course of immunosuppression and these grafts functioned for >100days with no further immunosuppression. In previous studies, we found the CD4+T cells from tolerant rats that transfer tolerance to an irradiated DA host grafted with a PVG heart, lose their tolerance transferring ability after 3days of culture, either with or without donor alloantigen, and effect rejection of specific-donor grafts. If cultures with specific-donor alloantigen are supplemented by supernatant from ConA activated lymphocytes the tolerance transferring cells survive, suggesting these cells depend on cytokines for their survival. In this study, we found addition of rIFN-γ to MLC with specific-donor alloantigen maintained the capacity of tolerant CD4+T cells to transfer alloantigen-specific tolerance and their ability to suppress PVG allograft rejection mediated by co-administered naïve CD4+T cells. IFN-γ suppressed the in vitro proliferation of tolerant CD4+T cells. Tolerant CD4+CD25+T cells did not proliferate in MLC to PVG stimulator cells with no cytokine added, but did when IFN-γ was present. IFN-γ did not alter proliferation of tolerant CD4+CD25+T cells to third-party Lewis. Tolerant CD4+CD25+T cells' expression of IFN-γ receptor (IFNGR) was maintained in culture when IFN-γ was present. This study suggested that IFN-γ maintained tolerance mediating alloantigen-specific CD4+CD25+T cells.