CD4+ regulatory T cells generated in vitro with IFN-{gamma} and allogeneic APC inhibit transplant arteriosclerosis

Foxp3+ regulatory T cell therapy for tolerance in autoimmunity and solid organ transplantation

Regulatory T cells (Tregs) are critical for tolerance in humans. The exact mechanisms by which the loss of peripheral tolerance leads to the development of autoimmunity and the specific role Tregs play in allograft tolerance are not fully understood; however, this population of T cells presents a unique opportunity in the development of targeted therapeutics. In this review, we discuss the potential roles of Foxp3+ Tregs in the development of tolerance in transplantation and autoimmunity, and the available data regarding their use as a treatment modality.

T cell phenotype in paediatric heart transplant recipients

Paediatric heart transplantation recipients suffer an increased incidence of infectious, autoimmune and allergic problems. The relative roles of thymus excision and immunosuppressive treatments in contributing to these sequelae are not clear. We compared the immunological phenotypes of 25 heart transplant recipients (Tx), 10 children who underwent thymus excision during non-transplantation cardiac surgery (TE) and 25 age range-matched controls, in two age bands: 1-9 and 10-16 years. Significant differences from controls were seen mainly in the younger age band with Tx showing lower CD3 and CD4 cell counts whilst TE showed lower CD8 cell counts. Naïve T cell and recent thymic emigrant proportions and counts were significantly lower than controls in both groups in the lower age band. T cell recombination excision circle (TREC) levels were lower than controls in both groups in both age bands. There were no differences in regulatory T cells, but in those undergoing thymus excision in infancy, their proportions were higher in TE than Tx, a possible direct effect of immunosuppression. T cell receptor V beta spectratyping showed fewer peaks in both groups than in controls (predominantly in the older age band). Thymus excision in infancy was associated with lower CD8 cell counts and higher proportions of Tregs in TE compared to Tx. These data are consistent with thymus excision, particularly in infancy, being the most important influence on immunological phenotype after heart transplantation.

Transplant arteriosclerosis in humanized mice reflects chronic lung allograft dysfunction and is controlled by regulatory T cells

OBJECTIVE

Chronic lung allograft dysfunction (CLAD) is a severe complication of lung transplantation limiting long-term survival. We studied correlations between CLAD after clinical lung transplantation and leukocyte-mediated development of transplant arteriosclerosis (TA) in a humanized mouse model. The pericardiophrenic artery was procured from surplus tissue of donor lungs (n = 22) transplanted in our clinical program and was implanted into the abdominal aorta of immune-deficient mice.

METHODS

Allogeneic human peripheral blood mononuclear cells (PBMCs) had been procured 1 day after lung transplantation from the respective recipients with or without enriching for CD4⁺CD25^high T cells were used. TA was assessed in mice 28 days later by histology. The respective clinical lung recipients were later divided into 2 groups. Eight patients (36.3%) had developed CLAD 23 ± 5 months after lung transplantation, whereas the remaining 14 (63.6%) did not develop CLAD within 25 ± 5 months.

RESULTS

In the PBMC CLAD+ group of mouse experiments, TA was significantly more severe than in the PBMC CLAD- group (39.9% ± 13% vs 14.9% ± 4% intimal thickening; P = .0081). Then, intimal thickening was significantly inhibited in the PBMC+ regulatory T cells CLAD+ group compared with the PBMC CLAD+ group (0.4% ± 4% vs 39.9% ± 13%; P = .003). In the experiments using PBMCs from lung recipients without CLAD, enriching regulatory T cells also suppressed the development of TA (0.9% ± 3% PBMC CLAD- vs 14.9% ± 4% PBMC+ regulatory T cells CLAD-; P = .001).

CONCLUSIONS

Lung transplant recipients who later develop CLAD have peripheral leukocytes already at the time of transplant that transfer proinflammatory properties leading to TA in a humanized mouse model. TA remains sensitive to inhibition by autologous regulatory T cells, suggesting a cell therapy-based approach for the prevention of CLAD after lung transplantation.

Regulatory T Cell and Forkhead Box Protein 3 as Modulators of Immune Homeostasis

The transcription factor forkhead box protein 3 (FOXP3) is an essential molecular marker of regulatory T cell (Treg) development in different microenvironments. Tregs are cells specialized in the suppression of inadequate immune responses and the maintenance of homeostatic tolerance. Studies have addressed and elucidated the role played by FOXP3 and Treg in countless autoimmune and infectious diseases as well as in more specific cases, such as cancer. Within this context, the present article reviews aspects of the immunoregulatory profile of FOXP3 and Treg in the management of immune homeostasis, including issues relating to pathology as well as immune tolerance.

IFNy+ and IFNy- Treg subsets with stable and unstable Foxp3 expression in kidney transplant recipients with good long-term graft function

BACKGROUND

Treg are a heterogenous cell population. In the present study we attempted to identify Treg subsets that might contribute to stable and good long-term graft function.

METHOD

Lymphocyte and Treg subsets were studied in 136 kidney transplant recipients with good long-term graft function and in 52 healthy control individuals using eight-color-fluorescence flow cytometry. Foxp3 TSDR methylation status was investigated in enriched IFNy+ and IFNy- Treg preparations using high resolution melt analysis.

RESULTS

Compared with healthy controls, patients showed strong associations of IFNy secreting Helios+ and Helios- Treg with Treg that co-expressed perforin and/or CTLA4 (CD152; p<0.01). Moreover they showed associations of IFNy-Helios+ Treg with Treg that produced TGFβ and/or perforin and of IFNy-Helios- Treg with TGFβ production (all p<0.01). Only in patients, but not in healthy controls, were IFNy- Helios+ and Helios- Treg associated with higher CD45+, CD3+, (CD4+), CD19+ lymphocyte counts (p<0.001). In addition IFNy-Helios+ Treg were associated with CD16+56+ lymphocytes (p<0.001). Enriched IFNy- Treg from female but not male patients showed an association of Foxp3 methylation with higher total Treg and higher Helios+IFNy-, CXCR3+Lselectin+ (CD183+CD62L+), CXCR3-Lselectin+ and CD28+HLADR+ Treg subsets (p<0.01). Enriched IFNy+ Treg from male patients showed an association of demethylated Foxp3 with total Treg and IL10-TFGβ+ Treg counts, and in enriched IFNy- Treg an association of methylated Foxp3 with APO1/FasR+FasL+ (CD95+CD178+) Treg (p<0.01).

CONCLUSIONS

Kidney recipients with good long-term graft function possess IFNy+ and IFNy- Treg with stable and unstable Foxp3 expression in the blood. They co-express CD28, HLADR, CTLA4, CXCR3, Lselectin, TGFβ, perforin and FasL and might contribute to the establishment and maintenance of good long-term graft function.

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.

Interferon-gamma producing regulatory T cells as a diagnostic and therapeutic tool in organ transplantation

There is increasing evidence that IFNg plays a major role in both induction of Tregs as well as immunosuppression mediated by IFNg-producing Tregs. The present review focuses on a small subset of iTregs that produces IFNg, comprises only 0.04% of all CD4(+) T lymphocytes in the blood of healthy individuals, and increases strongly during an immune response. IFNg(+) Tregs are induced by IFNg and IL12, making them sensors for inflammatory cytokines. They develop rapidly during inflammation and represent the first line of Tregs that suppress initial immune responses. The pool of IFNg(+) Tregs consists of activated stable immunosuppressive thymus-derived nTregs as well as peripherally proliferating iTregs with in part only transient immunosuppressive function, which limits their diagnostic and therapeutic usefulness in organ transplantation. Apparently, a part of IFNg(+) Tregs dies during the immune response, whereas others, after efficient immunosuppression with resolution of the immune response, differentiate toward Th1 lymphocytes. Goals of further research are the development of appropriate diagnostic tests for rapid and exact determinination of immunosuppressive IFNg(+) iTregs, as well as the induction and propagation of stable immunosuppressive IFNg(+) Tregs that establish and maintain good long-term graft function in transplant recipients.

Delayed anti-CD3 therapy results in depletion of alloreactive T cells and the dominance of Foxp3+ CD4+ graft infiltrating cells

The engineered Fc-nonbinding (crystallizable fragment-nonbinding) CD3 antibody has lower mitogenicity and a precise therapeutic window for disease remission in patients with type 1 diabetes. Before anti-CD3 can be considered for use in transplantation, the most effective timing of treatment relative to transplantation needs to be elucidated. In this study anti-CD3F(ab')2 fragments or saline were administered intravenously for 5 consecutive days (early: d1-3 or delayed: d3-7) to mice transplanted with a cardiac allograft (H2(b)-to-H2(k); d0). Survival of allografts was prolonged in mice treated with the early protocol (MST = 48 days), but most were rejected by d100. In contrast, in mice treated with the delayed protocol allografts continued to survive long term. The delayed protocol significantly inhibited donor alloreactivity at d30 as compared to the early protocol. A marked increase in Foxp3(+) T cells (50.3 ± 1.6%) infiltrating the allografts in mice treated with the delayed protocol was observed (p < 0.0001 vs. early (24.9 ± 2.1%)) at d10; a finding that was maintained in the accepted cardiac allografts at d100. We conclude that the timing of treatment with anti-CD3 therapy is critical for inducing long-term graft survival. Delaying administration effectively inhibits the alloreactivity and promotes the dominance of intragraft Foxp3(+) T cells allowing long-term graft acceptance.

T regulatory cell therapy in transplantation: stability, localization and functional specialization

PURPOSE OF REVIEW

There is great hope that cellular therapy with regulatory T cells (Tregs) will be an effective way to induce alloantigen specific tolerance, ultimately allowing for reduction or elimination of nonspecific immunosuppression. In the past, considerable effort was focused on defining the optimal ways to isolate and expand Tregs from peripheral or cord blood. Now that expansion of therapeutically relevant numbers of Tregs is feasible, we need to consider what is going to happen to the cells when they are transferred in vivo.

RECENT FINDINGS

For optimal function, Tregs must be able to traffic to the correct location(s) and, despite the presence of immunosuppressive therapy, live long enough to transfer their regulatory function to recipient T cells. Within the Treg pool, there are also functionally specialized subsets, identified by chemokine receptor expression and/or cytokine production, which control their trafficking and relative ability to suppress different types of T helper cells, respectively. Recent findings imply that the plasticity of appropriately obtained populations of Tregs may not be of as great concern as previously suggested. Experimental data have also provided evidence as to how one might design adjunctive treatment that best supports the viability and function of Tregs after transfer.

SUMMARY

Knowledge of how Tregs work in transplantation comes from studies that do not recapitulate how these cells will be used in humans. There is a need to develop better preclinical models to study how the in-vivo function of human Tregs can be optimized to ensure they can meet the challenge of inducing transplantation tolerance.

In-vitro inhibition of IFNγ+ iTreg mediated by monoclonal antibodies against cell surface determinants essential for iTreg function

Background

IFNγ-producing CD4⁺CD25⁺Foxp3⁺ PBL represent a subtype of iTreg that are associated with good long-term graft outcome in renal transplant recipients and suppress alloresponses in-vitro. To study the mechanism of immunosuppression, we attempted to block cell surface receptors and thereby inhibited the function of this iTreg subset in-vitro using monoclonal antibodies and recombinant proteins.

Methods

PBL of healthy control individuals were stimulated polyclonally in-vitro in the presence of monoclonal antibodies or recombinant proteins against/of CD178, CD152, CD279, CD28, CD95, and HLA-DR. Induction of IFNγ⁺ iTreg and proliferation of effector cells was determined using four-color fluorescence flow cytometry. Blockade of iTreg function was analyzed using polyclonally stimulated co-cultures with separated CD4⁺CD25⁺CD127^-IFNγ⁺ PBL.

Results

High monoclonal antibody concentrations inhibited the induction of CD4⁺CD25⁺Foxp3⁺IFNγ⁺ PBL (anti-CD152, anti-CD279, anti-CD95: p < 0.05) and CD4⁺CD25⁺CD127^-IFNγ⁺ PBL (anti-CD178, anti-CD152, anti-CD279, anti-CD95: p < 0.05). Effector cell proliferation increased with increasing antibody concentrations in culture medium (anti-CD178 and anti-CD279: p < 0.05). Conversely, high concentrations of recombinant proteins induced formation of CD4⁺CD25⁺Foxp3⁺IFNγ⁺ PBL (rCD152 and rCD95: p < 0.05) and decreased cell proliferation dose-dependently (rCD178 and rCD95: p < 0.05). Our data suggest an inverse association of iTreg induction with effector cell proliferation in cell culture which is dependent on the concentration of monoclonal antibodies against iTreg surface determinants. 3-day co-cultures of polyclonally stimulated PBL with separated CD4⁺CD25⁺CD127^-IFNγ⁺ PBL showed lower cell proliferation than co-cultures with CD4⁺CD25⁺CD127^-IFNγ^- PBL (p < 0.05). Cell proliferation increased strongly in CD4⁺CD25⁺CD127^-IFNγ^- PBL-containing co-cultures in the presence of monoclonal antibody (anti-CD28, anti-CD152, anti-CD279: p < 0.05) but remained low in co-cultures with CD4⁺CD25⁺CD127^-IFNγ⁺ PBL (with the exception anti-CD28 monoclonal antibody: p < 0.05). Monoclonal antibodies prevent iTreg induction in co-cultures with CD4⁺CD25⁺CD127^-IFNγ^- PBL but do not efficiently block suppressive iTreg function in co-cultures with CD4⁺CD25⁺CD127^-IFNγ⁺ PBL.

Conclusions

CD178, CD152, CD279, CD28, CD95, and HLA-DR determinants are important for induction and suppressive function of IFNγ⁺ iTreg.

Intimal hyperplasia: slow but deadly

Intimal hyperplasia is the leading cause of long-term failure in coronary artery bypass vein grafting, coronary artery stenting, angioplasty, arteriovenous fistula for dialysis, and allograft transplantation. Intimal hyperplasia is a product of vascular smooth muscle cell proliferation, migration through the internal elastic lamina, and deposition of extracellular matrix proteins driven by growth factors in the vasculature. This vascular pathology results in a progressive diminution of the vessel lumen and serves as a site for thrombosis and atherosclerotic lesions. A key cell type in the initiation of intimal hyperplasia is the vascular endothelial cell, which appears to have down-stream effects on the vascular smooth muscle proliferation and migration. Currently, the only means available for prevention of intimal hyperplasia is through inhibition of mammalian target of rapamycin (mTOR) with the immunosuppressant rapamycin. mTOR integrates up-stream signals from growth factors such as IL-2 and senses the cellular nutrient and energy levels and redox status. This presentation will discuss the potential means of preserving the vascular endothelial cell and, thereby, reducing the development of intimal hyperplasia in our open-heart surgical patients.

Regulatory T cells as modulators of chronic allograft dysfunction

Chronic allograft dysfunction (CAD) in solid organ transplantation is a principal cause of patient morbidity and late allograft loss. The pathogenesis of CAD is largely secondary to chronic damage by the adaptive immune system and long-term immunosuppression. Manipulating these factors may be possible with the use of regulatory T cells (Treg), which have the ability to suppress specific immune responses and therefore potentially remove the need for immunosuppressive drugs. Studies of CAD in experimental models have demonstrated the capacity for both mouse and human Treg cellular therapy to prevent the development of some manifestations of CAD. Furthermore, a role for Treg has been demonstrated in clinically tolerant transplant patients. Certain immunosuppressive therapies are also proving to be 'Treg friendly' and may be helpful in promoting Treg while maintaining other immunosuppressive activity. With this in mind, monitoring for biomarkers of operational tolerance with tailored immunosuppressive therapy or controlled weaning in conjunction with Treg cellular therapy may be a useful strategy to pursue.

Regulatory T cells in transplantation

T Regulatory cells (Treg) play an important role in the induction and maintenance of immunological tolerance to self and alloantigens. Recent findings in experimental transplant models have demonstrated that Treg can control acute and delayed allograft rejection. Preclinical attempts to use Treg as a cellular therapy have been successfully undertaken demonstrating the safety and feasibility of such treatment, suggesting that they have therapeutic potential.

Neutralizing IL-6 reduces human arterial allograft rejection by allowing emergence of CD161+ CD4+ regulatory T cells

Perioperative injuries to an allograft exacerbate graft rejection, which in humans is primarily mediated by effector memory T cells. IL-6 transcripts in human coronary artery segments rapidly increase posttransplantation into immunodeficient mouse hosts compared with those of pretransplant specimens and fall dramatically by 30 d. Adoptive transfer of human PBMCs allogeneic to the artery 2 d postoperatively results in T cell infiltrates and intimal expansion 4 wk later. Ab neutralization of human IL-6 reduces the magnitude of intimal expansion and total T cell infiltration but increases the relative expression of CD161 while decreasing other Th17 markers. Coculture of MHC class II-expressing human endothelial cells (ECs) with allogeneic CD4(+) memory T cells results in T cell activation and EC secretion of IL-6. Neutralizing IL-6 in primary allogeneic T cell-EC cocultures results in enhanced T cell proliferation of CD161(+) CD4(+) T cells, reduces total T cell proliferation upon restimulation in secondary cultures (an effect dependent on CD161(+) T cells), increases expression of FOXP3 in CD161(+) T cells, and generates T cells that suppress proliferation of freshly isolated T cells. These data suggest that IL-6 released from injured allograft vessels enhances allogeneic T cell infiltration and intimal expansion in a model of human allograft rejection by inhibiting an increase in CD161(+) regulatory T cells.

Moving to tolerance: clinical application of T regulatory cells

Decreasing the incidence of chronic rejection and reducing the need for life-long immunosuppression remain important goals in clinical transplantation. In this article, we will review how regulatory T cells (Treg) came to be recognized as an attractive way to prevent or treat allograft rejection, the ways in which Treg can be manipulated or expanded in vivo, and the potential of in vitro expanded/generated Treg for cellular therapy. We will describe the first regulatory T cell therapies that have been or are in the process of being conducted in the clinic as well as the safety concerns of such therapies and how outcomes may be measured.

Subsets of human CD4(+) regulatory T cells express the peripheral homing receptor CXCR3

Regulatory T cells (Tregs) migrate into peripheral sites of inflammation such as allografts undergoing rejection, where they serve to suppress the immune response. In this study, we find that ∼30-40% of human CD25(hi) FOXP3(+) CD4(+) Tregs express the peripheral CXC chemokine receptor 3 (CXCR3) and that this subset has potent immunoregulatory properties. Consistently, we observed that proliferative responses as well as IFN-γ production were significantly higher using CXCR3-depleted versus undepleted responders in the mixed lymphocyte reaction, as well as following mitogen-dependent activation of T cells. Using microfluidics, we also found that CXCR3 was functional on CXCR3(pos) Tregs, in as much as chemotaxis and directional persistence towards interferon-γ-inducible protein of 10 kDa (IP-10) was significantly greater for CXCR3(pos) than CXCR3(neg) Tregs. Following activation, CXCR3-expressing CD4(+) Tregs were maintained in vitro in cell culture in the presence of the mammalian target of rapamycin (mTOR) inhibitor rapamycin, and we detected higher numbers of circulating CXCR3(+) FOXP3(+) T cells in adult and pediatric recipients of renal transplants who were treated with mTOR-inhibitor immunosuppressive therapy. Collectively, these results demonstrate that the peripheral homing receptor CXCR3 is expressed on subset(s) of circulating human Tregs and suggest a role for CXCR3 in their recruitment into peripheral sites of inflammation.

Immunologic unresponsiveness to alloantigen in vivo: a role for regulatory T cells

Exposure to alloantigen in vivo or in vitro induces alloantigen reactive regulatory T cells that can control transplant rejection. The mechanisms that underpin the activity of alloantigen reactive regulatory T cells in vivo are common with those of regulatory T cells that prevent autoimmunity. The identification and characterization of regulatory T cells that control rejection and contribute to the induction of immunologic unresponsiveness to alloantigens in vivo has opened up exciting opportunities for new therapies in transplantation. Findings from laboratory studies are informing the design of clinical protocols using regulatory T cells as a cellular therapy.

CD4+ regulatory T cells in solid organ transplantation

PURPOSE OF REVIEW

Solid organ transplantation is the most effective treatment for end-stage organ failure, but the long-term outcomes remain suboptimal. CD4 regulatory T cells (Tregs) are emerging as a potential therapy to facilitate long-term allograft survival. This review provides a general overview of the biology of CD4 Tregs and then goes on to discuss the most relevant and recent experimental and clinical evidence for their therapeutic use in solid organ transplantation.

RECENT FINDINGS

There have been major advances in our understanding of Tregs, including improvements in methods for their isolation and expansion. Experimental models are providing very important data on the in-vitro and in-vivo behavior of Tregs in transplantation, while recent clinical trials of Treg cellular therapy in graft-versus-host disease are offering a valuable insight into the efficacy of Treg adoptive cellular therapy.

SUMMARY

Data in favor of Treg cellular therapy in transplantation are mounting, and we predict that their use in clinical trials is on the horizon.