IFN-gamma production by alloantigen-reactive regulatory T cells is important for their regulatory function in vivo

Decrease of Foxp3+ Treg cell number and acquisition of effector cell phenotype during lethal infection

Using a model of lethal oral infection with Toxoplasma gondii, we examined the fate of both induced and natural regulatory T (Treg) cells in the face of strong inflammatory responses occurring in a tolerogenic-prone environment. We found that during highly T helper 1 (Th1) cell-polarized mucosal immune responses, Treg cell numbers collapsed via multiple pathways, including blockade of Treg cell induction and disruption of endogenous Treg cell homeostasis. In particular, shutdown of interleukin 2 (IL-2) in the highly Th1 cell-polarized environment triggered by infection directly contributes to Treg cell incapacity to suppress effector responses and eventually leads to immunopathogenesis. Furthermore, we found that environmental cues provided by both local dendritic cells and effector T cells can induce the expression of T-bet transcription factor and IFN-gamma by Treg cells. These data reveal a mechanism for Th1 cell pathogenicity that extends beyond their proinflammatory program to limit Treg cell survival.

IL-15 promotes regulatory T cell function and protects against diabetes development in NK-depleted NOD mice

IL-15, an anti-apoptotic cytokine, has been reported to promote the survival and function of NK cells and T cells, including regulatory T cells (Tregs). Here we examined the effect of repeated injections of IL-15 on the development of diabetes in NOD mice. Injection of recombinant murine IL-15, once a day for 2 weeks, neither inhibited nor accelerated diabetes development in untreated NOD mice. However, treatment with IL-15 significantly reduced the incidence and delayed the onset of diabetes in NOD mice that were depleted of NK cells, while NK cell depletion alone had no protection against the disease development. The protective effect in IL-15-treated, NK cell-depleted NOD mice was associated with an increase in immunosuppressive activity of CD4(+)CD25(+) Tregs. IL-15 also enhanced Foxp3 expression in CD4(+)CD25(+) cells in an in vitro culture system, and such an effect of IL-15 was abrogated by IL-15-activated NK cells. Inhibition of IL-15-induced Foxp3 expression by IL-15-activated NK cells likely resulted from their IFN-gamma production, as recombinant IFN-gamma, or the culture supernatant of IL-15-activated wild-type mouse NK cells but not of IL-15-activated IFN-gamma-deficient NK cells, mediated a similar inhibition. IFN-gamma also diminished the stimulatory effect of IL-15 on Treg function in vitro. These results indicate that IL-15 has the potential to promote Treg function and protect against diabetes development in NOD mice, but such an activity can be eliminated by simultaneous activation of NK cells in IL-15-treated mice.

Donor reactive regulatory T cells

PURPOSE OF REVIEW

Donor reactive regulatory T cells (Treg) play an important role in tolerance induction and maintenance in experimental transplant models. In this review we focus on the formation of the donor reactive Treg pool and explore the potential of these cells for therapeutic application in clinical transplantation.

RECENT FINDINGS

Donor reactive Treg can arise by both conversion of alloreactive nonregulatory cells and expansion of naturally occurring Treg (nTreg) cross-reactive with donor alloantigen but the quantitative contribution of each of these pathways is at present unclear. However, the fact that donor reactive Treg can be driven both in vivo and ex vivo by alloantigen challenge of nonregulatory precursors is encouraging as it demonstrates that the functional potential of these cells for use in clinical transplantation will not be limited by fortuitous cross-reactivity between nTreg and donor alloantigens. Treg can be generated in vivo by transplantation or alloantigen challenge in combination with Treg-permissive immunosuppression, or ex vivo by phenotypic selection or by polyclonal or antigen-specific stimulation. A number of ex-vivo protocols exist for the enrichment of Treg in the laboratory and in many cases these cells have demonstrable function both in vitro and in relevant graft-versus-host disease (GVHD) or organ transplant models. The challenge now is to understand the clinical opportunities and limitations that these populations present.

SUMMARY

Combined with appropriate immunosuppression, Treg generated/expanded in vivo or ex vivo may hold the final key to operational tolerance in clinical setting.

Association of high IFN-gamma plasma levels with low B-cell counts in renal transplant recipients with stable long-term graft function

Recently, we reported that patients with long-term stable good graft function had higher interferon-gamma (IFN-gamma) and lower IL-4 plasma levels late as compared with early post-transplant. These patients had more often detectable CD3(+)CD4(+)CD25(+)IFN-gamma(+)Foxp3(+) peripheral blood lymphocytes (PBL) late post-transplant than patients with impaired graft function. We therefore speculated that high plasma IFN-gamma late post-transplant might contribute to the maintenance of graft acceptance. Using ELISA and four-color flow cytometry, plasma cytokines and PBL subpopulations were measured in 65 renal transplant recipients with stable graft function late post-transplant. High IFN-gamma plasma levels were associated with low CD19(+) B PBL (r = -0.329; p = 0.009) and low activated CD3(+)CD8(+)DR(+) T PBL (r = -0.266; p = 0.035). Plasma IFN-gamma increased with time post-transplant (r = 0.288; p = 0.022) and was not associated with the dose of immunosuppressive drugs (p = n.s.). High plasma IFN-gamma was not associated with serum creatinine (r = 0.038; p = 0.765). Five patients showed evidence of chronic allograft nephropathy in previous biopsies and none of them exhibited increased plasma IFN-gamma. In patients with good long-term graft function, high IFN-gamma plasma levels were associated with low numbers of B PBL and activated CD8(+) T PBL. High IFN-gamma plasma levels might prevent the development of an immunological alloresponse and thereby contribute to the maintenance of graft acceptance.

Separating graft-versus-leukemia from graft-versus-host disease in allogeneic hematopoietic stem cell transplantation

Routine methods to maximize the graft-versus-leukemia (GvL) activity of allogeneic hematopoietic stem cell transplantation (HSCT) without the detrimental effects of graft-versus-host disease (GvHD) are lacking. Depletion or inhibition of alloreactive T cells is partially effective in preventing GvHD, but usually leads to decreased GvL activity. The current model for the pathophysiology of acute GvHD describes a series of immune pathways that lead to activation of donor T cells and inflammatory cytokines responsible for tissue damage in acute GvHD. This model does not account for how allotransplant can lead to GvL effects without GvHD, or how the initial activation of donor immune cells may lead to counter-regulatory effects that limit GvHD. In this review, we will summarize new findings that support a more complex model for the initiation of GvHD and GvL activities in allogeneic HSCT, and discuss the potential of novel strategies to enhance GvL activity of the transplant.

Expression and function of immunoglobulin-like transcripts on tolerogenic dendritic cells

The expression of inhibitory immunoglobulin-like transcripts (ILTs) on dendritic cells (DCs) is a biomarker of tolerogenic DCs. In this article we discuss current knowledge on the function of ILTs and explore the molecular mechanisms involved in modulation of DCs via the inhibitory receptor and its natural ligand, rendering these cells tolerogenic. We propose a method to enhance targeting of inhibitory receptors on DCs using microparticles containing a preferential ligand, HLA-G, and monoclonal antibody against the pan-DCs marker CD11c. The double-coated microparticles increase the binding of ILT4 receptor and improve modulation of DCs in vitro and in vivo. This targeting concept can be used for regulation of specific immune responses to antigens in transplantation, autoimmunity, allergy, and cancer.

IL-10 interferes directly with TCR-induced IFN-gamma but not IL-17 production in memory T cells

IL-10 is a potent immunoregulatory and anti-inflammatory cytokine. However, therapeutic trials in chronic inflammation have been largely disappointing. It is well established that IL-10 can inhibit Th1 and Th2 cytokine production via indirect effects on APC. Less data are available about the influence of IL-10 on IL-17 production, a cytokine which has been recently linked to chronic inflammation. Furthermore, there are only few reports about a direct effect of IL-10 on T cells. We demonstrate here that IL-10 can directly interfere with TCR-induced IFN-gamma production in freshly isolated memory T cells in the absence of APC. This effect was independent of the previously described effects of IL-10 on T cells, namely inhibition of IL-2 production and inhibition of CD28 signaling. In contrast, IL-10 did not affect anti-CD3/anti-CD28-induced IL-17 production from memory T cells even in the presence of APC. This might have implications for the interpretation of therapeutic trials in patients with chronic inflammation where Th17 cells contribute to pathogenesis.

Interleukin-12 family members and type I interferons in Th17-mediated inflammatory disorders

Cytokines produced by antigen-presenting cells govern the fate of helper T-cell responses. Herein, we review the impact of interleukin (IL)-23 and IL-27 on the outcome of T-helper (Th) 17 cell responses and discuss their impact in the pathogenesis of T-cell-mediated inflammatory disorders of autoimmune or allergic origin. We then discuss how type I interferons might influence the course of autoimmune diseases by tipping the balance between IL-12 family members.

BTLA targeting modulates lymphocyte phenotype, function, and numbers and attenuates disease in nonobese diabetic mice

The novel coinhibitory receptor BTLA may have a regulatory role in maintaining peripheral tolerance; however, its role in autoimmune diabetes is unknown. In this study, we show that anti-BTLA mAb 6F7 selectively depleted pathogenic B and CD4+ T(H) cells; enhanced the proportion of cells with the forkhead box p3+ PD-1+CD4+ regulatory T phenotype; and increased the production of potentially protective (IL-10) and detrimental (IL-2, IFN-gamma) cytokines in NOD mice. As interactions between BTLA and PD-1 coinhibitory pathways have been described in the cardiac allograft model, we also investigated if these pathways may have significant interaction in autoimmune diabetes. Anti-BTLA inhibited anti-PD-1-potentiated total IL-12 (p40+p70) production, suggesting the possibility that anti-BTLA may have a greater effect in the setting of anti-PD-1-triggered diabetes. To test this, NOD mice at 4 and 10 weeks of age were treated with anti-BTLA mAb, anti-PD-1 mAb, both mAb, or isotype control and were monitored for diabetes development. Although anti-BTLA mAb delayed diabetes onset significantly in 10- but not 4-week-old NOD mice, anti-BTLA mAb attenuated anti-PD-1-induced diabetes in both age groups. Hence, strategies targeting BTLA+ lymphocytes or therapies enhancing the BTLA-negative cosignal may prove valuable in treating autoimmune diabetes.

Interleukin 17-producing T helper cells in alloimmunity

Interleukin (IL) 17 is a proinflammatory cytokine already known to play a defense role against microbes and a pathogenic role in a number of autoimmune diseases. Although IL-17 can be produced by a variety of cells including neutrophils, CD8+, NK, and gamma-delta T cells, the concept of IL-17-secreting CD4+ T helper cells (Th17), distinct from Th1 and Th2, recently emerged. Herein, we discuss arguments in favor of a Th17-mediated alternative pathway of allograft rejection based on clinical and experimental observations drawn from the literature. We also discuss the complex interplays among regulatory T cells and Th17 cells in the allogeneic context.

Paradoxical effects of IFN-gamma in graft-versus-host disease reflect promotion of lymphohematopoietic graft-versus-host reactions and inhibition of epithelial tissue injury

Interferon-gamma (IFN-gamma) inhibits graft-versus-host disease (GVHD) in lethally irradiated mice receiving allogeneic hematopoietic cell transplantation (allo-HCT) but promotes lethality in unirradiated and sublethally irradiated recipients. We investigated the role of IFN-gamma in GVHD in sublethally irradiated B6D2F1 recipients of B6 allo-HCT. B6D2F1 mice receiving wild-type B6 splenocytes alone died rapidly, whereas those receiving wild-type B6 splenocytes plus marrow survived long-term. Mice in both groups showed rapid elimination of host hematopoietic cells but minimal parenchymal tissue injury. However, mice receiving allo-HCT from IFN-gamma-deficient donors died rapidly regardless of whether donor marrow was given, and they exhibited severe parenchymal injury but prolonged survival of host hematopoietic cells. IFN-gamma plays a similar role in another model involving delayed B6 donor leukocyte infusion (DLI) to established mixed allogeneic (B6-->BALB/c) chimeras. IFN-gamma promotes DLI-mediated conversion from mixed to full donor chimerism while attenuating GVHD. Importantly, IFN-gamma enhances graft-versus-leukemia (GVL) effects in both models. Our data indicate that previously reported IFN-gamma-induced early mortality in allo-HCT recipients is due to augmentation of lymphohematopoietic graft-versus-host reaction (LGVHR) and can be avoided by providing an adequate source of donor hematopoietic stem/progenitor cells. Furthermore, the magnitude of GVL is correlated with the strength of LGVHR, and IFN-gamma reduces the potential of this alloreactivity to cause epithelial tissue GVHD.

Manipulation of indoleamine 2,3-dioxygenase (IDO) for clinical transplantation: promises and challenges

BACKGROUND

Since the discovery that indoleamine 2,3-dioxygenase (IDO) is a modulator for maintenance of fetomaternal immuno-privilege state, it has been implicated in tumour tolerance, autoimmune diseases and asthma. IDO is an IFN-gamma-inducible, intracellular enzyme that catalyzes the initial and rate-limiting step in the degradation of tryptophan. It has been suggested that IDO can regulate the immune system either through deprivation of tryptophan that is essential for T cell proliferation or via cytotoxic effects of kynurenine pathway metabolites on T cell survival.

METHODS

The sources of information used were obtained through Pubmed/Medline.

RESULTS/CONCLUSION

While IDO emerges as a regulator of immunity, its role in controlling allo-response is unfolding. IDO can control T cell responses to allo-antigens and induce generation of allo-specific regulatory T cells. Exploiting IDO as a modulator of transplant rejection, many groups have manipulated its activity to prolong allograft survival in transplantation models. Despite the initial promise, its application to clinical transplantation may be limited. We therefore examine the potentials and limitations associated with clinical translation of IDO into a therapeutic.

Alloantigen specific T regulatory cells in transplant tolerance

CD4(+)CD25(+)Foxp3(+)T cells are regulatory/suppressor cells (Treg) that include non-antigen(Ag)-specific as well as Ag-specific Tregs. How non-Ag-specific naïve CD4(+)CD25(+)Treg develop into specific Tregs is unknown. We have studied DA rats tolerant to fully allogeneic PVG cardiac grafts that survived with out immunosuppression for over 100 days and identified the cellular basis of alloantigen specific tolerance. Key observations from our studies will be reviewed including how CD4(+)CD25(+)Tregs were first identified and the cytokine dependence of CD4(+)T cells that transfer alloantigen specific transplant tolerance which died in culture unless stimulated with both cytokine rich ConA supernatant and specific donor alloantigen. Both the tolerant CD4(+)CD25(+) and CD4(+)CD25(-) T cell populations are required to transfer tolerance, yet alone the CD4(+)CD25(-) T cell effect rejection. Tolerance transfer occurs with a low ratio of CD4(+)CD25(+)T cells (<1:10), whereas to induce tolerance with naive CD4(+)CD25(+)T cells requires both a ratio of >1:1 and is not alloantigen specific. Recent findings on how naïve CD4(+)CD25(+)T cells developed into two separated pathways of alloantigen specific Tregs, by culturing them with alloAg with either IL-2 or IL-4 and donor alloantigen are described. IL-2 enhances IFN-gammaR and IL-5 mRNA while IL-4 induced a reciprocal profile with de novo IL-5Ralpha and increased IFN-gamma mRNA expression. Both IL-2 and IL-4 alloactivated CD4(+)CD25(+)Tregs within 3-4 days of culture can induce alloantigen specific tolerance at ratios of 1:10. Long term, CD4(+)CD25(+)T cells from tolerant hosts given IL-2 cultured cells have increased IL-5 and IFN-gammaR mRNA; whereas hosts given IL-4 cultured cells had enhanced IL-5Ralpha mRNA expression and IL-5 enhanced their proliferation to donor but not third party alloAg. These findings suggest that Th1 and Th2 responses activate two pathways of alloantigen specific Tregs that can mediate transplant tolerance but are dependent upon cytokines produced by ongoing Th1 and/or Th2 immune responses.

C1q enhances IFN-gamma production by antigen-specific T cells via the CD40 costimulatory pathway on dendritic cells

Dendritic cells (DCs) are known to produce C1q, the initiator of the classical complement pathway. We demonstrate that murine DCs deficient in C1q (C1qa(-/-)) are poorer than wild-type (WT) DCs at eliciting the proliferation and Th1 differentiation of antigen-specific T cells. These defects result from decreased production of IL-12p70 by C1qa(-/-) DCs and impaired expression of costimulatory molecules CD80 and CD86 in response to CD40 ligation. The defective production of IL-12p70 and the reduced expression of CD80 and CD86 by C1qa(-/-) DCs were specifically mediated via CD40 ligation, as normal levels of IL-12p70 and CD80/86 were observed after ligation of Toll-like receptors (TLRs) on C1qa(-/-) DCs. CD40 ligation on C1qa(-/-) DCs, but not TLR ligation, results in decreased phosphorylation of p38 and ERK1/2 kinases. A strong colocalization of CD40 and C1q was observed by confocal microscopy upon CD40 ligation (but not TLR ligation) on DCs. Furthermore, human DCs from 2 C1q-deficient patients were found to have impaired IL-12p70 production in response to CD40L stimulation. Our novel data suggest that C1q augments the production of IL-12p70 by mouse and human DCs after CD40 triggering and plays important roles in sustaining the maturation of DCs and guiding the activation of T cells.

TGF-beta and kynurenines as the key to infectious tolerance

The maintenance of self-tolerance is an integral part of the immune surveillance process, in which cytokines act as master regulators of a complex network involving multiple cell types. On such cytokines, transforming growth factor-beta (TGF-beta) exerts a suppressive control over immune reactivity, which so far appears to be mostly confined to the T-cell compartment. Recently, dendritic cells (DCs) have been found to be both an early source and a target of TGF-beta actions. In these cells, autocrine, paracrine and T-cell-derived TGF-beta activates the tolerogenic pathway of tryptophan catabolism - mediated by indoleamine 2,3-dioxygenase (IDO) - resulting in a burst of regulatory kynurenines that contribute to establishing a state of 'infectious tolerance'. Current molecular insights suggest a synergistic potential for TGF-beta and IDO in physiologically or therapeutically opposing human pathologies sustained by over-reacting immune responses.

CD4+CD25+ T cells alloactivated ex vivo by IL-2 or IL-4 become potent alloantigen-specific inhibitors of rejection with different phenotypes, suggesting separate pathways of activation by Th1 and Th2 responses

CD4(+)CD25(+)Foxp3(+) T cells are regulatory/suppressor cells (Tregs) that include non-antigen (Ag)-specific as well as Ag-specific Tregs. How non-Ag-specific naive CD4(+)CD25(+) Treg develop into specific Tregs is unknown. Here, we generated adaptive Tregs by culture of naive CD4(+)CD25(+)Foxp3(+) T cells with allo-Ag and either interleukin-2 (IL-2) or IL-4. Within days, IL-2 enhanced interferon-gamma receptor (Ifngammar) and Il-5 mRNA and IL-4 induced a reciprocal profile with de novo IL-5Ralpha and increased IFN-gamma mRNA expression. Both IL-2- and IL-4-alloactivated CD4(+)CD25(+) Tregs within 3 to 4 days of culture had enhanced capacity to induce tolerance to specific donor but not to third-party cardiac allografts. These hosts became tolerant as allografts functioned more than 250 days, with a physiologic ratio of less than 10% CD4(+)CD25(+)Foxp3(+) T cells in the CD4(+) population. CD4(+)CD25(+) T cells from tolerant hosts given IL-2-cultured cells had increased Il-5 and Ifngammar mRNA. Those from hosts given IL-4-cultured cells had enhanced IL-5Ralpha mRNA expression and IL-5 enhanced their proliferation to donor but not third-party allo-Ag. Thus, IL-2 and IL-4 activated allo-Ag-specific Tregs with distinct phenotypes that were retained in vivo. These findings suggested that T-helper 1 (Th1) and Th2 responses activate 2 pathways of adaptive Ag-specific Tregs that mediate tolerance. We propose they be known as T-suppressor 1 (Ts1) and Ts2 cells.

IFN-gamma dictates allograft fate via opposing effects on the graft and on recipient CD8 T cell responses

CD8 T cells are necessary for costimulation blockade-resistant rejection. However, the mechanism by which CD8 T cells mediate rejection in the absence of major costimulatory signals is poorly understood. IFN-gamma promotes CD8 T cell-mediated immune responses, but IFN-gamma-deficient mice show early graft loss despite costimulation blockade. In contrast, we found that IFN-gamma receptor knockout mice show dramatically prolonged graft survival under costimulation blockade. To investigate this paradox, we addressed the effects of IFN-gamma on T cell alloresponses in vivo independent of the effects of IFN-gamma on graft survival. We identified a donor-specific CD8 T cell breakthrough response temporally correlated with costimulation blockade-resistant rejection. Neither IFN-gamma receptor knockout recipients nor IFN-gamma-deficient recipients showed a CD8 breakthrough response. Graft death on IFN-gamma-deficient recipients despite costimulation blockade could be explained by the lack of IFN-gamma available to act on the graft. Indeed, the presence of IFN-gamma was necessary for graft survival on IFN-gamma receptor knockout recipients, as either IFN-gamma neutralization or the lack of the IFN-gamma receptor on the graft precipitated early graft loss. Thus, IFN-gamma is required both for the recipient to mount a donor-specific CD8 T cell response under costimulation blockade as well as for the graft to survive after allotransplantation.

Upregulation of molecules associated with T-regulatory function by thymoglobulin pretreatment of human CD4+ cells

BACKGROUND

This study evaluated the immunologic effects of thymoglobulin in modulating human CD4+ cells.

METHODS

Human CD4+ cells were purified from peripheral blood mononuclear cells by negative selection method. CD4+ cells were pretreated with thymoglobulin and incubated for 72 hr. Cells and culture supernatants were collected and studied by real-time quantitative polymerase chain reaction, fluorescence activated cell scanning, multiplex cytokine assay, and mixed lymphocyte reaction (MLR).

RESULTS

Thymoglobulin pretreated CD4+ cells demonstrated up-regulation of gene transcripts for CTLA-4, OX40, forkhead box P3 (Foxp3), CD25, IFN-gamma, IL-10, and IL-2 as determined by real-time quantitative polymerase chain reaction. Fluorescence-activated cell scanning analysis demonstrated that CD4+ cells, pretreated with thymoglobulin, up-regulated CD25 expression on their surface, and the surface expression of CTLA-4 and OX40 and the expression of intracellular Foxp3 were observed in these CD4+CD25+ cells. Additionally, MLR demonstrated that thymoglobulin-pretreated cells partially inhibited proliferation of untreated autologous CD4+ cells in response to allogeneic cells. The high levels of IFN-gamma, IL-10, IL-2, and IL-4 were detected by multiplex cytokine assay in supernatants collected from cultures of thymoglobulin-pretreated CD4+ cells. The lymphocyte proliferation of allogeneic MLR was also partially blocked in the presence of supernatants from cultures of thymoglobulin-pretreated CD4+ cells.

CONCLUSIONS

This study demonstrates that the unique effects of thymoglobulin in modulating CD4+ cells may be an important mechanism for its action in inducing immunosuppression and transplant tolerance.

Aspirin and the induction of tolerance by dendritic cells

Tolerance is maintained by central and peripheral regulatory mechanisms and is essential to prevent autoimmunity. In the setting of solid organ or haematopoietic transplantation, the indirect pathway of allorecognition is a significant driver of chronic rejection. Chronic rejection proceeds despite effective immunosuppressive therapy, therefore achieving immunological tolerance to control the indirect pathway is a desirable goal. Tolerance induction may be achieved by vaccination with modified antigen presenting cells (APCs). Mature dendritic cells (DCs) are potent APCs, but immature DCs have been shown to have a reduced allo-stimulatory capacity and can be tolerogenic. Drug treatment has been shown to decrease the allo-stimulatory capacity of DC compared to immature DC. Dexamethasone and vitamin D3 have been established as having potent effects on dendritic cell immunogenicity.The effects of aspirin, a non-steroidal anti-inflammatory, on DCs have not previously been so extensively studied and here we will review the work which has been carried out using aspirin to induce tolerogenic DCs.We have examined the mechanisms of tolerance induction using human DCs and T cells. It has been possible to demonstrate that in aspirin treated, human DCs there is inhibition of the nuclear factor K-B (NFKB) signalling pathway, modified cytokine production, reduced expression of co-stimulatory molecules (CD40, CD80, and CD86) and increased expression of immunoglobulin-like transcript-3 (ILT3). The decreased expression of co-stimulatory molecules is maintained following cytokine or lipopolysaccharide (LPS) challenge. Drug treatment of DCs increases the expression of immunoglobulin-like transcript 3 (ILT3) when compared with immature DCs (iDCs), and these high levels of expression are maintained when the cells are challenged with a maturational stimulus. Aspirin also reduces the allo-stimulatory capacity of human DCs, and induces hypo-responsiveness and regulatory activity in responder T cells. These regulatory T-cells were CD4(+) CD25(+) FOXP3(+) and by studying CD25(-) or CD45RA populations, it was possible to determine that these regulatory T cells were generated de novo rather than requiring the expansion of naturally occurring Tregs. Aspirin continues therefore to be of interest with regard its wider effects on immune regulation, other than that mediated by direct inhibition of cyclo-oxygenase, in particular its ability to induce tolerogenic DCs at therapeutic concentrations in humans.

IL-12R beta 2 promotes the development of CD4+CD25+ regulatory T cells

We have previously shown that mice lacking the IL-12-specific receptor subunit beta2 (IL-12Rbeta2) develop more severe experimental autoimmune encephalomyelitis than wild-type (WT) mice. The mechanism underlying this phenomenon is not known; nor is it known whether deficiency of IL-12Rbeta2 impacts other autoimmune disorders similarly. In the present study we demonstrate that IL-12Rbeta2(-/-) mice develop earlier onset and more severe disease in the streptozotocin-induced model of diabetes, indicating predisposition of IL-12Rbeta2-deficient mice to autoimmune diseases. T cells from IL-12Rbeta2(-/-) mice exhibited significantly higher proliferative responses upon TCR stimulation. The numbers of naturally occurring CD25(+)CD4(+) regulatory T cells (Tregs) in the thymus and spleen of IL-12Rbeta2(-/-) mice were comparable to those of WT mice. However, IL-12Rbeta2(-/-) mice exhibited a significantly reduced capacity to develop Tregs upon stimulation with TGF-beta, as shown by significantly lower numbers of CD25(+)CD4(+) T cells that expressed Foxp3. Functionally, CD25(+)CD4(+) Tregs derived from IL-12Rbeta2(-/-) mice were less efficient than those from WT mice in suppressing effector T cells. The role of IL-12Rbeta2 in the induction of Tregs was confirmed using small interfering RNA. These findings suggest that signaling via IL-12Rbeta2 regulates both the number and functional maturity of Treg cells, which indicates a novel mechanism underlying the regulation of autoimmune diseases by the IL-12 pathway.

Interleukin-12 family members and the balance between rejection and tolerance

PURPOSE OF REVIEW

Allograft rejection involves multiple effector mechanisms. Interleukin(IL)-12 family members play a critical role in influencing helper T-cell differentiation and inflammatory processes, and their respective role in orchestrating inflammation of autoimmune or infectious origin starts to be unravelled. We highlight recent findings on the function of the different IL-12 family members: IL-12p70, IL-23, IL-27 and IL-35 and discuss their possible involvement in influencing the balance between graft rejection and tolerance.

RECENT FINDINGS

The capacity of dendritic cells to produce IL-12 and IL-23 strongly influences the outcome of CD4 T-cell responses. While the IL-12/interferon-gamma axis has classically been involved in autoimmune pathologies and acute graft rejection, it is now clear that it also displays immunoregulatory properties. In contrast, IL-23 promotes the function of proinflammatory IL-17-producing cells in both mice and humans. Both IL-27 and IL-35 have recently emerged as important regulators of adaptive immune responses.

SUMMARY

The contribution of the IL-12/interferon-gamma pathway to acute graft rejection may be more complicated than initially thought. As our understanding of the IL-12 family is rapidly growing and changing, the respective role of its members in orchestrating innate and adaptive immune responses toward alloantigens should be addressed.

Exogenous IFN-gamma ex vivo shapes the alloreactive T-cell repertoire by inhibition of Th17 responses and generation of functional Foxp3+ regulatory T cells

Interferon (IFN)-γ was originally characterized as a pro-inflammatory cytokine with T helper type 1-inducing activity, but subsequent work has demonstrated that mice deficient in IFN-γ or IFN-γ receptor show exacerbated inflammatory responses and accelerated allograft rejection, suggesting that IFN-γ also has important immunoregulatory functions. Here, we demonstrate that ex vivo IFN-γ conditioning of CD4 T cells driven by allogeneic immature dendritic cells (DC) results in the emergence of a Foxp3⁺ regulatory T-cell (Treg)- dominant population that can prevent allograft rejection. The development of this population involves conversion of non-Treg precursors, preferential induction of activation-induced cell death within the non-Treg population and suppression of Th2 and Th17 responses. The suppressive activity of IFN-γ is dependent on the transcription factor signal transducer and activator of transcription 1 and is mediated by induced nitric oxide. These data indicate not only how IFN-γ could be used to shape beneficial immune responses ex vivo for possible cell therapy but also provide some mechanistic insights that may be relevant to exacerbated inflammatory responses noted in several autoimmune and transplant models with IFN-γ deficiency.

Interferon-gamma conditioning ex vivo generates CD25+CD62L+Foxp3+ regulatory T cells that prevent allograft rejection: potential avenues for cellular therapy

BACKGROUND

Regulatory T cells (Treg) play important roles in preventing autoimmunity, graft-versus host disease and transplant rejection. In rodent transplant models, tolerance induction strategies can induce graft protective CD25CD4 Treg in vivo but therapeutic exploitation of active regulation will more likely depend on protocols that allow generation or selection of regulatory cells ex vivo for use as a cellular therapy. We have used adoptive transfer skin and islet allograft models to identify, develop and evaluate ex vivo protocols that generate donor-reactive, adaptive Treg.

METHODS

Naïve CDA CD4 T cells were stimulated with allogeneic antigen-presenting cell under neutral conditions or with cytokine modification, restimulated under identical conditions and subsequently analyzed for cytokine profile, phenotypic markers characteristic of Treg and in vivo regulatory function.

RESULTS

Without modification, CD4 T cells default to a Th2 phenotype characterized by a dominant interleukin-4 response which is profoundly detrimental to allograft survival. However, addition of exogenous interferon-gamma suppresses interleukin-4 production without priming for effector function, induces suppressor of cytokine signaling-1 and results in up-regulation of Foxp3 and CD62L. The generation of these populations is enhanced by, but is independent of, the presence of naturally occurring endogenous Treg. Most importantly, when tested for regulatory function in vivo, these cells prevent rejection of both skin and islet allografts mediated by effector T cells.

CONCLUSIONS

These data reveal an unexpected role for interferon-gamma in the generation of Treg ex vivo and suggest a possible route for the generation of regulatory cells for therapeutic use.

OX40/OX40L costimulation affects induction of Foxp3+ regulatory T cells in part by expanding memory T cells in vivo

OX40 is a member of the TNFR superfamily and has potent T cell costimulatory activities. OX40 also inhibits the induction of Foxp3(+) regulatory T cells (Tregs) from T effector cells, but the precise mechanism of such inhibition remains unknown. In the present study, we found that CD4(+) T effector cells from OX40 ligand-transgenic (OX40Ltg) mice are highly resistant to TGF-beta mediated induction of Foxp3(+) Tregs, whereas wild-type B6 and OX40 knockout CD4(+) T effector cells can be readily converted to Foxp3(+) T cells. We also found that CD4(+) T effector cells from OX40Ltg mice are heterogeneous and contain a large population of CD44(high)CD62L(-) memory T cells. Analysis of purified OX40Ltg naive and memory CD4(+) T effector cells showed that memory CD4(+) T cells not only resist the induction of Foxp3(+) T cells but also actively suppress the conversion of naive CD4(+) T effector cells to Foxp3(+) Tregs. This suppression is mediated by the production of IFN-gamma by memory T cells but not by cell-cell contact and also involves the induction of T-bet. Importantly, memory CD4(+) T cells have a broad impact on the induction of Foxp3(+) Tregs regardless of their origins and Ag specificities. Our data suggest that one of the mechanisms by which OX40 inhibits the induction of Foxp3(+) Tregs is by inducing memory T cells in vivo. This finding may have important clinical implications in tolerance induction to transplanted tissues.

The effects of immunosuppression on regulatory CD4(+)CD25(+) T cells: impact on immunosuppression selection in transplantation

During immune response and T-cell activation, both effector T cells and regulatory T(T(reg)) cells are activated and regulated simultaneously by both positive and negative pathways. CD4(+)CD25(+) T(reg) cells play a critical role in immune tolerance to self antigens as well as to allografts in some transplant settings. Effective immunosuppressive regimens significantly reduced the incidence of acute allograft rejection in patients following organ transplantation. However, the impact of immunosuppressive treatment on the potential induction of transplant tolerance has not been well determined. In this review we summarize the effects of immunosuppressive reagents on CD4(+)CD25(+) T(reg) cells in order to bring attention to this issue, which may affect the choice of immunosuppressive regimen in the clinical setting.

Evolving immunosuppressive microenvironment during human cervical carcinogenesis

Chronic infection with human papillomavirus (HPV) can result in cervical cancer. To understand how HPV escapes immune eradication, we examined biophenotypes of immune cells in human normal cervix, cervical intraepithelial neoplasia (CIN), and cancer. Expression and cellular localization of Forkhead box protein-3 (FOXP3), indolamine 2,3-dioxygenase (IDO), interleukin (IL)-10, and interferon (IFN)-gamma were examined by immunofluorescence and immunohistochemistry. Mean cell densities of stromal FOXP3+ cells, IDO+ cells, IL-10+ cells, CD1a+ cells, and macrophages significantly increased from normal cervix to cancer, whereas densities of IFN-gamma+ and MMP-9+ cells increased from normal cervix to CIN but decreased in cancer. Flow cytometry confirmed significant elevation of cervical T cells expressing IFN-gamma and transforming growth factor-beta in CIN compared with normal cervix. Upon activation, a significantly increased proportion of cervical T cells expressed IFN-gamma in CIN than normal. A unique subset of morphologically immature stromal dendritic cells expressing IL-10 and IDO was more numerous in cancer than in normal cervix and CIN. The potentially suppressive immune milieu in the cervix may be permissive of HPV-associated cervical carcinogenesis.

Stable transgene expression from HSV amplicon vectors in the brain: potential involvement of immunoregulatory signals

The herpes simplex virus (HSV) amplicon is a plasmid-based, infectious gene delivery system that carries up to 150 kilobase (kb) of exogenous DNA. We previously characterized early host responses and stability of transgene expression in mice systemically injected with HSV amplicon vectors. Transgene expression was readily detected primarily in the liver but rapidly declined to undetectable levels within 2 weeks. Molecular analyses revealed induction of type I interferons (IFN) as the primary response, and early transcriptional silencing of the vector followed IFN's activation of signal transducers and activators of transcription 1 (STAT1). In this study, we investigate vector administration by stereotactic injection into the striatum. In the brain, induction of type I IFN was rather modest, and transgene expression lasted more than 1 year despite dose-dependent inflammation and infiltration of immune cells around injection sites. Further analyses revealed dose-dependent upregulation of immunosuppressive cytokines and molecular markers specific to regulatory T cells in the injected brain regions, which supported the immune-privileged properties of the brain parenchyma. Overall, our findings indicate that the spectrum of host responses can differ significantly depending on target organs and administrative routes, and that HSV amplicon vectors hold great potential for gene therapy of chronic neurological disorders.

Exosomes from bronchoalveolar fluid of tolerized mice prevent allergic reaction

Exosomes are nanovesicles originating from multivesicular bodies that are secreted by a variety of cell types. The dual capability of exosomes to promote immunity or to induce tolerance has prompted their clinical use as vehicles for vaccination against different human diseases. In the present study, the effect of allergen-specific exosomes from tolerized mice on the development of allergen-induced allergic response was determined using a mouse model. Mice were tolerized by respiratory exposure to the olive pollen allergen Ole e 1. Exosome-like vesicles were isolated from bronchoalveolar lavage fluid of the animals by the well-established filtration and ultracentrifugation procedure, characterized by electron microscopy, Western blot, and FACS analyses, and assessed in a prophylactic protocol. To this end, BALB/c mice were intranasally treated with tolerogenic exosomes or naive exosomes as control, 1 wk before sensitization/challenge to Ole e 1. Blood, lungs, and spleen were collected and analyzed for immune responses. Intranasal administration of tolerogenic exosomes inhibited the development of IgE response, Th2 cytokine production, and airway inflammation--cardinal features of allergy--and maintained specific long-term protection in vivo. This protective effect was associated with a concomitant increase in the expression of the regulatory cytokine TGF-beta. These observations demonstrate that exosomes can induce tolerance and protection against allergic sensitization in mice. Thus, exosome-based vaccines could represent an alternative to conventional therapy for allergic diseases in humans.

CD4+CD25+ regulatory T cells have divergent effects on intestinal inflammation in IL-10 gene-deficient mice

The regulatory effect of murine CD4+CD25+ T-cells in vivo appears to be dependent on the secretion of IL-10. The lack of IL-10 in the IL-10 gene-deficient mouse has a profoundly negative effect on the mouse's regulation of the response to intestinal bacteria, resulting in severe enterocolitis. We investigated the effect of neonatal injection with wild-type CD4+CD25+ T-cells on the intestinal immune response in IL-10 gene-deficient mice. At the time of analysis, 8-15 weeks later, all mice demonstrated an increased, antigen-stimulated systemic response. However, the intestinal response was divergent with about half of the mice developing an intestinal inflammation with a high injury score, the other half demonstrating a remarkable reduction in injury score with a marked decrease in intestinal IFNgamma release. Our data demonstrate that CD4+CD25+ T-cells can be activated in IL-10 gene-deficient mice and that this stimulation under stringent conditions has the potential to reduce intestinal inflammation.

Opposing effects of interferon-alpha and interferon-gamma on the expression of major histocompatibility complex class I chain-related A in tumors

Natural killer cells are an important component of innate resistance to viruses, bacteria, certain parasites, and tumors. The activating receptor natural killer group 2D (NKG2D) plays a critical role in the elimination of tumor cells by cytotoxic effector cells. It has been shown that the strength of an antitumor immune response might be critically dependent on NKG2D ligard surface levels. Thus, it is essential to regulate the expression of NKG2D ligands in order to ensure effective tumor immunosurveillance and the elimination of pathogen-infected cells. In the present study, we found that interferon (IFN)-alpha and IFNgamma exert opposing effects on major histocompatibility complex class I-related chain A (MICA) expression in human tumor cells. IFNalpha promotes expression of the NKG2D ligand MICA in tumor cells and therefore enhances their sensitivity to natural killer lysis. In contrast, IFNgamma exerts the opposite effect. IFNalpha promotes MICA expression at the level of transcription by augmenting MICA promoter activity. IFNgamma modulates MICA expression not only at the transcriptional level, but also at the post-translational level by promoting proteolytic cleavage by matrix metalloproteinases. Further study is needed to clarify the precise regulatory mechanisms. The pathways involved in NKG2D ligand induction might represent a promising target for improving immune responses to cancer or infections.

Manipulating the immune system for anti-tumor responses and transplant tolerance via mixed hematopoietic chimerism

SUMMARY

Stem cells (SCs) with varying potentiality have the capacity to repair injured tissues. While promising animal data have been obtained, allogeneic SCs and their progeny are subject to immune-mediated rejection. Here, we review the potential of hematopoietic stem cells (HSCs) to promote immune tolerance to allogeneic and xenogeneic organs and tissues, to reverse autoimmunity, and to be used optimally to cure hematologic malignancies. We also review the mechanisms by which hematopoietic cell transplantation (HCT) can promote anti-tumor responses and establish donor-specific transplantation tolerance. We discuss the barriers to clinical translation of animal studies and describe some recent studies indicating how they can be overcome. The recent achievements of durable mixed chimerism across human leukocyte antigen barriers without graft-versus-host disease and of organ allograft tolerance through combined kidney and bone marrow transplantation suggest that the potential of this approach for use in the treatment of many human diseases may ultimately be realized.

CD11b+ monocytes abrogate Th17 CD4+ T cell-mediated experimental autoimmune myocarditis

Experimental autoimmune myocarditis (EAM) represents a Th17 T cell-mediated mouse model of postinflammatory heart disease. In BALB/c wild-type mice, EAM is a self-limiting disease, peaking 21 days after alpha-myosin H chain peptide (MyHC-alpha)/CFA immunization and largely resolving thereafter. In IFN-gammaR(-/-) mice, however, EAM is exacerbated and shows a chronic progressive disease course. We found that this progressive disease course paralleled persistently elevated IL-17 release from T cells infiltrating the hearts of IFN-gammaR(-/-) mice 30 days after immunization. In fact, IL-17 promoted the recruitment of CD11b(+) monocytes, the major heart-infiltrating cells in EAM. In turn, CD11b(+) monocytes suppressed MyHC-alpha-specific Th17 T cell responses IFN-gamma-dependently in vitro. In vivo, injection of IFN-gammaR(+/+)CD11b(+), but not IFN-gammaR(-/-)CD11b(+), monocytes, suppressed MyHC-alpha-specific T cells, and abrogated the progressive disease course in IFN-gammaR(-/-) mice. Finally, coinjection of MyHC-alpha-specific, but not OVA-transgenic, IFN-gamma-releasing CD4(+) Th1 T cell lines, together with MyHC-alpha-specific Th17 T cells protected RAG2(-/-) mice from EAM. In conclusion, CD11b(+) monocytes play a dual role in EAM: as a major cellular substrate of IL-17-induced inflammation and as mediators of an IFN-gamma-dependent negative feedback loop confining disease progression.

Niflumic acid renders dendritic cells tolerogenic and up-regulates inhibitory molecules ILT3 and ILT4

Niflumic acid is a member of non-steroidal anti-inflammatory agents, from which aspirin was recently shown to inhibit maturation of human-monocyte derived dendritic cells (DCs). DCs are crucial regulators of the immune response, capable of inducing immunity as well as tolerance. In our in vitro study we showed a tolerogenic effect of NFA on phenotype and function of LPS-matured monocyte-derived DCs. Different drug concentrations dose-dependently down-regulated the expression of co-stimulatory molecules, particularly CD80 and lowered the expression of dendritic cell marker CD1a. Opposingly, the expressions of two inhibitory surface molecules, associated with tolerogenic DCs, immunoglobulin-like transcripts (ILT)3 and ILT4 were induced in treated DCs. The levels of TNFalpha production by NFA-treated DCs did not change significantly compared to controls, whereas the IL-12p70 and IL-10 production was completely abrogated at higher drug concentrations. However, at lower drug concentrations, the production of IL-12p70 was increased. There were no significant differences in the uptake of FITC labeled dextran by treated DCs compared to untreated cells. In allogeneic cultures with whole CD4+ T cells, dendritic cells differentiated in the presence of NFA appeared poor stimulators of CD4+ T-cell proliferation, even compared to immature DCs (iDCs). These results indicate the immunosuppressive properties of NFA, which may be therapeutically useful in controlling chronic immune and/or inflammatory diseases, by modulating DC characteristics towards tolerogenic DCs.

Gene expression profiling on acute rejected transplant kidneys with microarray

To investigate the gene expression profiles in acute allograft rejection of renal transplantation, and identify the markers for the early diagnosis of acute rejection, heterotopic kidney transplantation was performed by using F344 or Lewis donors and Lewis recipients. No immunosuppressant was used. Renal grafts were harvested on days 3, 7, and 14. A commercial microarray was used to measure gene expression levels in day-7 grafts. The expression levels of 48 genes were up-regulated in the allograft in comparison with the isograft control, and interferon-gamma-induced GTPase gene was most significantly up-regulated in allografts. It is concluded that a variety of pathways are involved in organ transplant rejection which is dynamic and non-balanced. IFN-inducible genes, such as IGTP, may play an important role in the rejection. A lot of important factors involved in acute rejection are unnecessary but sufficient conditions for the rejection. We are led to conclude that it is virtually impossible to make an early diagnosis based on a single gene marker, but it could be achieved on the basis of a set of markers.

The effects of tolerance on allograft damage caused by the innate immune system

BACKGROUND

It is not known whether tolerance can be induced in a strong proinflammatory milieu or whether the induction of tolerance can prevent interferon (IFN)-gamma-associated graft injury. To address these questions, we studied the effects of rIFN-gamma infusion on porcine cardiac allograft survival.

METHODS

Recombinant interferon (rIFN)-gamma was continuously infused into the left anterior descending artery of hearts transplanted into major histocompatibility complex-inbred miniature swine treated with a 12-day course of cyclosporine A. Group 1 recipients received a nearly syngeneic heart, group 2 recipients received a class I disparate heart, and group 3 recipients were cotransplanted with a class I-disparate heart and kidney, a procedure demonstrated to induce tolerance to both grafts. A fourth group of animals were not transplanted but received intracoronary rIFN-gamma infusion into the native heart.

RESULTS

rIFN-gamma perfusion not only accelerated the acute rejection of class I-disparate hearts (mean survival time, 19+/-7.21 vs. 38+/-8.19; P=0.025) but caused near-syngeneic heart transplants, which otherwise survived indefinitely, to reject within 35 days. In contrast, rIFN-gamma perfusion had no demonstrable effects on hearts grafts in tolerant recipients or on autologous hearts.

CONCLUSIONS

These results suggest that tolerance induction can occur in the presence of IFN-gamma-mediated inflammation, and that tolerance induction can prevent the tissue injury caused by the overproduction of IFN-gamma. This suggests that the beneficial effects of tolerance may include protection from nonspecific inflammatory responses, such as those produced by ischemia-reperfusion injury and brain death.

The Foxp3+ regulatory T cell: a jack of all trades, master of regulation

The function of regulatory T cells (T(reg) cells) has been attributed to a growing number of diverse pathways, molecules and processes. Seemingly contradictory conclusions regarding the mechanisms underlying T(reg) cell suppressive activity have revitalized skeptics in the field who challenge the core validity of the idea of T(reg) cells as central immune regulators. However, we note that a consensus may be emerging from the data: that multiple T(reg) cell functions act either directly or indirectly at the site of antigen presentation to create a regulatory milieu that promotes bystander suppression and infectious tolerance. Thus, the versatility and adaptability of the Foxp3+ T(reg) cells may in fact be the best argument that these cells are 'multitalented masters of immune regulation'.

Relative contribution of direct and indirect allorecognition in developing tolerance after liver transplantation

The interaction of donor passenger leukocytes and host leukocytes in recipient secondary lymphoid tissues during the early posttransplantation period is crucial in directing host immune reactions toward allograft rejection or acceptance. Responsible T cell clones could be activated through the direct and indirect pathways of allorecognition. We examined the role of the indirect pathway in liver transplantation (LT) tolerance by depleting host antigen-presenting cells (APC) with phagocytic activity [e.g., cluster domain (CD)68+/CD163+ macrophages, CD11c+ dendritic cells (DC)] using liposome-encapsulating clodronate (LP-CL). After Lewis rat cell or liver graft transplantation, Brown Norway (BN) rat recipients pretreated with LP-CL showed a significantly reduced type 1 helper T cell cytokine up-regulation than control-LP-treated recipients. In the LT model, LP-CL treatment and host APC depletion abrogated hepatic tolerance; Lewis liver grafts in LP-CL-treated-BN recipients developed mild allograft rejection, failed to maintain donor major histocompatibility complex (MHC) class II+ leukocytes, and developed chronic rejection in challenged donor heart allografts, while control-LP-treated BN recipients maintained tolerance status and donor MHC class II+ hepatic leukocytes. Furthermore, in the BN to Lewis LT model, LP-CL recipient treatment abrogated spontaneous hepatic allograft acceptance, and graft survival rate was reduced to 43% from 100% in the control-LP group. In conclusion, the study suggests that host cells with phagocytic activity could play significant roles in developing LT tolerance.

Observational support for an immunoregulatory role of CD3+CD4+CD25+IFN-gamma+ blood lymphocytes in kidney transplant recipients with good long-term graft outcome

There is evidence that interferon-gamma (IFN-gamma)-dependent interactions of dendritic cell (DC), T regulatory (Treg), and T suppressor (Ts) subpopulations contribute to allograft acceptance. We measured DC subsets, CD3+CD4+CD25+ (Treg phenotype) and CD3+CD8+CD28(-) (Ts phenotype) peripheral blood lymphocytes (PBL) expressing Foxp3, Th1 or Th2 cytokines, peripheral T- and B-cell counts, and plasma cytokines in 33 kidney transplant recipients with a serum creatinine of < or =1.8 mg/dl and 32 recipients with a serum creatinine of > or =2.0 mg/dl more than 100 days post-transplant. Cell subsets were measured in whole blood using four-color flow cytometry. Patients with increased creatinine had less frequently detectable CD3+CD4+CD25+IFN-gamma+ PBL than patients with good graft function (P = 0.017). In patients with good graft function, CD3+CD4+CD25+IFN-gamma+ PBL were associated with high Foxp3+, IL-2+, IL-12+, IL-4+, and IL-10+ CD3+CD4+CD25+ T PBL (P < 0.001), low CD3+CD8+CD28(-)Foxp3+ (P = 0.002), CD3+CD4+DR+ (P = 0.002), CD3+CD8+DR+ T (P = 0.005) and CD19+ B PBL (P = 0.005), and low lineage(-)HLA-DR+CD11c+CD123(-) DC1 (P = 0.006). Patients with impaired graft function did not show these associations. Additional flow cytometric analysis confirmed strong co-expression of IFN-gamma and Foxp3 by CD4+CD25+ PBL particularly in patients with good graft function. Our data support an immunoregulatory role of CD3+CD4+CD25+Foxp3+IFN-gamma+ cells in a subgroup of transplant recipients with good graft acceptance.