Expression patterns of regulatory T-cell markers in accepted and rejected nonhuman primate kidney allografts

Non-human Primate Regulatory T Cells and Their Assessment as Cellular Therapeutics in Preclinical Transplantation Models

Non-human primates (NHP) are an important resource for addressing key issues regarding the immunobiology of regulatory T cells (Treg), their in vivo manipulation and the translation of adoptive Treg therapy to clinical application. In addition to their phenotypic and functional characterization, particularly in cynomolgus and rhesus macaques, NHP Treg have been isolated and expanded successfully ex vivo. Their numbers can be enhanced in vivo by administration of IL-2 and other cytokines. Both polyclonal and donor antigen (Ag) alloreactive NHP Treg have been expanded ex vivo and their potential to improve long-term outcomes in organ transplantation assessed following their adoptive transfer in combination with various cytoreductive, immunosuppressive and "Treg permissive" agents. In addition, important insights have been gained into the in vivo fate/biodistribution, functional stability, replicative capacity and longevity of adoptively-transferred Treg in monkeys. We discuss current knowledge of NHP Treg immunobiology, methods for their in vivo expansion and functional validation, and results obtained testing their safety and efficacy in organ and pancreatic islet transplantation models. We compare and contrast results obtained in NHP and mice and also consider prospects for future, clinically relevant studies in NHP aimed at improved understanding of Treg biology, and innovative approaches to promote and evaluate their therapeutic potential.

An Evaluation of 20 Years of EU Framework Programme-Funded Immune-Mediated Inflammatory Translational Research in Non-Human Primates

Aging western societies are facing an increasing prevalence of chronic inflammatory and degenerative diseases for which often no effective treatments exist, resulting in increasing health-care expenditure. Despite high investments in drug development, the number of promising new drug candidates decreases. We propose that preclinical research in non-human primates can help to bridge the gap between drug discovery and drug prescription. Translational research covers various stages of drug development of which preclinical efficacy tests in valid animal models is usually the last stage. Preclinical research in non-human primates may be essential in the evaluation of new drugs or therapies when a relevant rodent model is not available. Non-human primate models for life-threatening or severely debilitating diseases in humans are available at the Biomedical Primate Research Centre (BPRC). These have been instrumental in translational research for several decades. In order to stimulate European health research and innovation from bench to bedside, the European Commission has invested heavily in access to non-human primate research for more than 20 years. BPRC has hosted European users in a series of transnational access programs covering a wide range of research areas with the common theme being immune-mediated inflammatory disorders. We present an overview of the results and give an account of the studies performed as part of European Union Framework Programme (EU FP)-funded translational non-human primate research performed at the BPRC. These data illustrate the value of translational non-human primate research for the development of new therapies and emphasize the importance of EU FP funding in drug development.

Lymphoid-Like Structures with Distinct B Cell Areas in Kidney Allografts are not Predictive for Graft Rejection. A Non-human Primate Study

Kidney allograft biopsies were analyzed for the presence of B cell clusters/aggregates using CD20 staining. Few B cells were found in the diffuse interstitial infiltrates, but clusters of B cells were found in nodular infiltrates. These nodular infiltrates were smaller shortly after transplantation, and their size increased over time. At the time of clinical rejection, the nodules often presented as tertiary lymphoid structures (TLS) with lymphoid-like follicles. The presence of small B cell clusters during the first 2 months after transplantation was not associated with early rejection. Even in animals that did not reject their allograft, TLS-like structures were present and could disappear over time. Although TLS were more often found in samples with interstitial fibrosis and tubular atrophy (IFTA), TLS were also present in samples without IFTA. The presence and density of clusters resembling tertiary lymphoid structures most likely reflect an ongoing immune response inside the graft and do not necessarily signify a poor graft outcome or IFTA.

Potential of T-regulatory cells to protect xenografts

PURPOSE OF REVIEW

Immunological barriers still preclude clinical xenotransplantation. The protective role of CD4(+)CD25(+)Foxp3(+) T-regulatory cells (Treg) in allotransplantation is well described and, therefore, could represent a promising therapeutical tool for xenotransplantation. This review addresses the latest findings on Treg in xenotransplantation research.

RECENT FINDINGS

In vivo, costimulation blockade-based strategies including anti-CD154 monoclonal antibodies (mAbs) in combination with rapamycin or anti-LFA-1 mAb prolonged both concordant and discordant islets xenografts survival in a Treg-dependent manner. In vitro, IL-10 secretion was shown to be critical for the suppression of xenogeneic responses mediated by Treg. Moreover, transgenic expression of inducible costimulator-immunoglobulin or PD-L1 on porcine endothelial cells inhibited human T-cell proliferation in vitro and was associated with the induction of Treg and IL-10 secretion. CXCR3 mediated the recruitment of Treg to pig endothelium. Finally, the recruitment of human Treg was enhanced by the immobilization of human CCL17 on pig endothelium.

SUMMARY

There is increasing evidence for the potential of CD4(+)CD25(+)Foxp3(+) Treg to protect xenografts. Induction of Treg in recipients and/or recruitment of human Treg to pig endothelium may represent novel strategies to prevent cell-mediated rejection in pig-to-human xenotransplantation.

Analysis of FOXP3 gene and protein expressions in renal allograft biopsies and their association with graft outcomes

BACKGROUND

The transcription factor FOXP3 is increased in acute renal rejection, but its influence on graft outcomes is unclear. This study correlated FOXP3 with dendritic cells and graft outcomes.

METHODS

We assessed 96 kidney transplants undergoing allograft biopsy for cause. FOXP3 mRNA was analyzed by real-time polymerase chain reaction (PCR) and FOXP3 protein and DCsCD83(+) by immunohistochemistry. Graft function and survival were assessed at 5 years post-transplantation, as well as by independent predictors of graft loss.

RESULTS

Intragraft FOXP3 gene and protein expression were significantly correlated (r = 0.541, p < 0.001). Both FOXP3 mRNA and protein were increased in patients with acute rejection (AR). High expression of FOXP3 mRNA or protein in biopsies did not correlate with clinical variables, but there was a trend to higher positive variation in the glomerular filtration rate (GFR) from biopsy to last follow-up. Patients with FOXP3-mRNA(high) had more DCsCD83(+) in biopsy, but these cells did not associate with AR. Five-year graft survival was not influenced by either FOXP3 mRNA or protein expressions.

CONCLUSIONS

FOXP3 mRNA and protein had a good correlation in archival renal graft tissue. Increased FOXP3 expression was found in AR and FOXP3 associated with high numbers of DCs. However, both FOXP3 mRNA and protein was not associated with better allograft outcomes.

Comparative analysis of inflammatory infiltrates in collagen-induced arthritis, kidney graft rejection and delayed-type hypersensitivity in non-human primates

OBJECTIVES

Non-human primates are immunologically closely related to humans providing relevant models of inflammatory disorders often used to evaluate new immunomodulating therapies. The aim of the study was to compare inflammatory infiltrates of acute graft rejection (AR) and collagen-induced arthritis (CIA) to delayed-type hypersensitivity (DTH) reactions as the latter model may serve as a less invasive animal model.

MATERIALS AND METHODS

Tissue samples of AR, CIA and DTH were obtained from rhesus monkeys used in several pre-clinical studies. The infiltrate composition was determined by immunohistochemical analysis.

RESULTS

The infiltrates in AR consisted of T cells, macrophages and B cells. The presence of lymphoid structures in AR suggested ongoing intragraft immune activation. The synovia of CIA contained predominantly macrophages and few T cells. The DTH infiltrates were dominated by T cells when the challenged was ovalbumin (OVA) and by macrophages when the challenge was tetanus toxoid (TT).

CONCLUSIONS

The histology of AR resembles aspects of DTH to OVA while that of CIA showed similarities of the DTH to TT. The DTH reaction could serve as a model to study immunomodulating drugs for acute rejection and the acute inflammatory phase of autoimmunity.

Determination of Absolute Counts of Circulating Regulatory T Cells in Cynomolgus Macaques Using an Optimized Flow Cytometric Method

Regulatory T cells (Tregs) are a rare subset of lymphocytes that inhibit the activation and effector functions of T cells and are important regulators of immune responses. Although Tregs are well characterized in humans and rodents, little is known about their immunophenotyping (IP) profile in cynomolgus macaques ( Macaca fascicularis), which is an important species for pharmacological and toxicological evaluation of potential immune modulators because of their similar physiologic, genetic, and metabolic response patterns to humans. The authors have developed an immunophenotyping panel using a high-throughput 96-well microtiter plate–based assay to detect circulating Tregs (CD3+CD4+CD25hiFoxP3+) and have determined the normal range for the number of Tregs in naive healthy cynomolgus macaques to be 56.4 to 179.7 cells/µL (mean ± SEM = 113.6 ± 5.1 cells/µL; n = 25). Furthermore, the authors compared the resulting FoxP3+ Treg profiles with a CD127lo cell-surface panel (CD3+CD4+CD25hi CD127lo) and found a close correlation between the absolute numbers of CD3+CD4+CD25hiFoxP3+ and CD3+CD4+CD25hiCD127lo cells (mean ± SD = 120 ± 8.0 cells/µL). Quantification of circulating Tregs in cynomolgus macaques in this high-throughput assay may help to identify drug candidates that affect this rare, but critical, immunoregulatory cell population.

FOXP3+ regulatory T cells: from suppression of rejection to induction of renal allograft tolerance

Naturally occurring and induced regulatory T cells (Tregs) can become hyporesponsive and anergic to antigen stimulation in autoimmune diseases and allograft rejection. The mechanisms of suppression of effector T cells by Tregs remain unclear, but there are in vitro and in vivo evidences showing that these cells are able to suppress antigen-specific responses via direct cell-to-cell contact, secrete anti-inflammatory cytokines such as TGF-β and IL-10, and inhibit the generation of memory T cells, among others. The transcription factor FOXP3 is a specific marker of Tregs and its deficiency is associated with autoimmune diseases and inflammation. During acute rejection of kidney allografts, an augmented FOXP3 gene expression as well as increased CD4(+)CD25(+)FOXP3(+) and other cell populations are observed in graft biopsies. However, it is not clear whether Tregs migrate into the graft and are retained there to suppress the inflammatory process, or whether they are directly associated with more complex mechanisms to induce immune tolerance. FOXP3(+) Tregs may direct the immune response toward a graft acceptance program, potentially affecting the long-term survival of transplanted organs and tissues. Immunosuppressive drugs modulate the number and function of circulating Tregs and FOXP3 expression. Experimental and clinical studies have shown that mTOR inhibitors have positive and calcineurin inhibitors negative effects on Tregs, but it is difficult to set apart the effect of multiple other factors known to be associated with short- and long-term renal graft outcomes. This review aimed to describe the functions of Tregs and its transcription factor FOXP3 in suppression of immune response during rejection and in induction of kidney graft tolerance, as well as to review the individual effects of immunosuppressive drugs on Tregs.

Non-human primate regulatory T cells: current biology and implications for transplantation

Regulatory T cells (Treg) offer potential for improving long-term outcomes in cell and organ transplantation. The non-human primate model is a valuable resource for addressing issues concerning the transfer of Treg therapy to the clinic. Herein, we discuss the properties of non-human primate Treg and prospects for their evaluation in allotransplantation and xenotransplantation.

Phenotypic and functional switch of macrophages induced by regulatory CD4+CD25+ T cells in mice

CD4(+)CD25(+) regulatory T cells (Treg cells) are important in maintenance of peripheral tolerance. The direct effect of CD4(+)CD25(+) Treg cells on macrophages was studied using a mouse model in which syngeneic CD4(+)CD25(+) Treg cells were adoptively transferred into the peritoneal cavity of SCID mice. Peritoneal macrophages in mice transferred with CD4(+)CD25(+) Treg cells expressed significantly higher levels of CD23, CD47 and CD206 and less CD80 and major histocompatibility complex class II molecules as compared with those mice that received either CD4(+)CD25(-) T cells or no cells. Macrophages of mice injected with CD4(+)CD25(+) Treg cells displayed a remarkably enhanced phagocytosis of chicken red blood cells, and arginase activity together with an increased interleukin-10 (IL-10) production, whereas they showed a decreased antigen-presenting ability and nitric oxide production. Furthermore, CD4(+)CD25(+) Treg cells and CD4(+)CD25(-) T cells showed strong antagonistic effects on macrophage polarizations in vivo. Blocking arginase, IL-10 and/or transforming growth factor-β (TGF-β) partially but significantly reversed the effects of CD4(+)CD25(+) Treg cells to induce M2 macrophages in vivo suggesting that CD4(+)CD25(+) Treg cells have the ability to induce M2 macrophages at least in part through arginase, IL-10 and TGF-β pathways. Thus, we have provided the in vivo evidence to support the unknown pathways for CD4(+)CD25(+) Treg cells to regulate innate immunity by promoting the differentiation of M2 macrophages as well as by inhibiting M1 macrophage induction by CD4(+)CD25(-) T cells in mice. CD4(+)CD25(+) Treg cells efficiently induced M2 macrophage differentiation in mice, offering the in vivo evidence to support the role of CD4(+)CD25(+) Treg cells in regulating innate immunity.

Anti-CD154 mAb and rapamycin induce T regulatory cell mediated tolerance in rat-to-mouse islet transplantation

Background

Anti-CD154 (MR1) monoclonal antibody (mAb) and rapamycin (RAPA) treatment both improve survival of rat-to-mouse islet xenograft. The present study investigated the effect of combined RAPA/MR1 treatment on rat-to-mouse islet xenograft survival and analyzed the role of CD4⁺CD25⁺Foxp3⁺ T regulatory cells (Treg) in the induction and maintenance of the ensuing tolerance.

Methodology/Principal Findings

C57BL/6 mice were treated with MR1/RAPA and received additional monoclonal anti-IL2 mAb or anti CD25 mAb either early (0–28 d) or late (100–128 d) post-transplantation. Treg were characterised in the blood, spleen, draining lymph nodes and within the graft of tolerant and rejecting mice by flow cytometry and immunohistochemistry. Fourteen days of RAPA/MR1 combination therapy allowed indefinite islet graft survival in >80% of the mice. Additional administration of anti-IL-2 mAb or depleting anti-CD25 mAb at the time of transplantation resulted in rejection (100% and 89% respectively), whereas administration at 100 days post transplantation lead to lower rejection rates (25% and 40% respectively). Tolerant mice showed an increase of Treg within the graft and in draining lymph nodes early post transplantation, whereas 100 days post transplantation no significant increase of Treg was observed. Rejecting mice showed a transient increase of Treg in the xenograft and secondary lymphoid organs, which disappeared within 7 days after rejection.

Conclusions/Significances

These results suggest a critical role for Treg in the induction phase of tolerance early after islet xenotransplantation. These encouraging data support the need of developing further Treg therapy for overcoming the species barrier in xenotransplantation.

Molecular phenotypes of acute rejection predict kidney graft prognosis

Earlier detection of antibody-mediated rejection of kidney allografts may improve graft outcomes. Profiling of gene expression holds promise for the diagnosis and prognosis of antibody-mediated rejection. Here, we identified 730 patients who received kidney transplants during 2002-2005, including 21 patients (2.9%) who experienced early acute antibody-mediated rejection. We also identified a matched group of 43 patients with early acute T cell-mediated rejection to serve as controls. Compared with patients with T cell-mediated rejection, those with antibody-mediated rejection had significantly higher intrarenal mRNA expression of the cytoprotective heme oxygenase-1 but had lower expression of the regulatory T cell marker forkhead box P3 (FoxP3), the B cell marker CD20, and the chemokine regulated upon activation, normal T cell expressed and secreted (RANTES). T cell infiltration was similar in both groups of patients. Compared with grafts that had a favorable course, those that failed as a result of antibody-mediated rejection had expression profiles suggesting a lack of regulation (less FoxP3, TGF-beta1, RANTES, and CD20). Grafts that failed as a result of T cell-mediated rejection only revealed lower expression of CD20 mRNA. In summary, these data suggest that severe antibody-mediated rejection and T cell-mediated rejection result in graft loss by distinct mechanisms. Molecular phenotypes of early acute rejection might help to identify grafts with poor prognosis, allowing earlier application of additional therapies.

FOXP3-enriched infiltrates associated with better outcome in renal allografts with inflamed fibrosis

BACKGROUND

FOXP3-expressing regulatory T cells (Tregs) play a crucial role in maintaining allogeneic transplant tolerance in experimental models. In clinical transplantation, there are few data about their role in chronic inflammation. We hypothesized that Tregs might accumulate within the graft since enrichment of Tregs has been frequently described in chronically inflamed tissues.

METHODS

Sixty-seven biopsies, indicated by a rise in creatinine level, were studied. Thirty-four biopsies showing acute T-cell-mediated rejection and 33 displaying inflamed fibrosis were selected. Tregs frequency was calculated for each infiltrate by counting FOXP3+ and CD3+ cells on two contiguous serial sections.

RESULTS

A total of 121 infiltrates were scored with a mean of 309 CD3+ cells per infiltrate (range: 50-700). Tregs were enriched within allografts exhibiting inflamed fibrosis versus acute cellular rejection (10.6 +/- 6.8% versus 5.5 +/- 2.6%, respectively, P = 0.005). In those with inflammation within scarred areas, the subset of patients with a low FOXP3/CD3 ratio (below the median value) displayed a lower frequency of B-cell-enriched nodular cell clusters (20% versus 86%, P = 0.001) and had a significantly lower graft survival (log-rank, P = 0.02). In multivariate analysis, the low FOXP3/CD3 ratio remained an independent indicator of outcome (P = 0.03). Consistently, the FOXP3+/IL-17+ cell ratio was higher in nodular than in diffuse infiltrates.

CONCLUSIONS

Our results suggest that Tregs may dampen the graft injury in chronic (versus acute) inflammation and stress the importance of devising strategies to enhance Tregs efficiency.

A monoclonal antibody selection for immunohistochemical examination of lymphoid tissues from non-human primates

Non-human primates (NHPs) offer valuable animal models for basic research into human diseases and for the preclinical validation of new therapeutics. Detailed in situ examination of the involved cell types using immunohistochemistry is often hampered by the lack of cross-reactive antibodies (Abs). In the current study, we have tested a large panel of monoclonal antibodies raised against human leukocyte differentiation and activation markers for cross-reactivity on cryosections of lymphoid tissue from six NHP species. In total, we have tested 130 Abs against 69 antigens expressed in tissues from one great ape species (chimpanzee/Pan troglodytes), two Old World species (rhesus macaque/Macaca mulatta and cynomolgus macaque/Macaca fascicularis), and three New World species (common marmoset/Callithrix jacchus, cotton-top tamarin/Saguinus oedipus, and owl monkey/Aotus triviogatus). We have found a large panel of cross-reactive Abs: 93 of 102 (91%) in chimpanzee, 97 of 125 (78%) in rhesus macaque, 70 of 109 (64%) in cynomolgus macaque, 69 of 116 (60%) in common marmoset, 40 of 81 (49%) in cotton-top tamarin, and 35 of 80 (44%) in owl monkey. The availability of a reliable panel of cross-reactive markers is important to gaining further insight into immunological processes in disease-affected tissues from NHP species.

Intragraft FOXP3 protein or mRNA during acute renal allograft rejection correlates with inflammation, fibrosis, and poor renal outcome

BACKGROUND

Forkhead box (FOXP3) is considered to be a specific marker for regulatory T cells. The aim of this study was to correlate intragraft FOXP3 at mRNA and cellular levels during renal allograft rejection to response to therapy and late clinical outcome.

METHODS

Immunostainings and quantitative reverse-transcriptase polymerase chain reaction for FOXP3, CD3, and transforming growth factor (TGF)-beta were performed and results were related to histopathologic and clinical outcome.

RESULTS

A good correlation between immunohistochemical analysis and mRNA levels for both CD3 and FOXP3 was observed. Intragraft FOXP3 was significantly related to tubulitis and interstitial fibrosis. A strong correlation was found between FOXP3 and CD3 mRNA and between FOXP3 and TGF-beta mRNA. No correlation was found between FOXP3 and response to therapy.

DISCUSSION

In conclusion, intragraft FOXP3 at both cellular and molecular levels parallels T-cell infiltration during acute rejection. FOXP3 does not predict response to antirejection therapy. FOXP3 correlates with renal fibrosis, TGF-beta, and poor late renal outcome.

Levels of Foxp3 in regulatory T cells reflect their functional status in transplantation

Foxp3 expressing CD4(+)CD25(+) regulatory T cells (Tregs) have been shown to prevent allograft rejection in clinical and animal models of transplantation. However, the role of Foxp3 in regulating Treg function, and the kinetics and mechanism of action of Tregs in inducing allograft tolerance in transplantation, are still not fully understood. Thus, we investigated the kinetics and function of Tregs in a mouse model of orthotopic corneal transplantation, the most common form of tissue grafting worldwide. In this study, using in vitro functional assays and in vivo Treg adoptive transfer assays, we show that far more relevant than Treg frequency is their level of Foxp3 expression, which is directly associated with the potential of Tregs to prevent allograft rejection by producing regulatory cytokines and suppressing effector T cell activation. In addition, our data clearly demonstrate that Tregs primarily suppress the induction of alloimmunity in regional draining lymph nodes rather than suppressing the effector phase of the immune response in the periphery. These findings provide new insights on Treg dynamics in transplantation, which are crucial for designing therapeutic strategies to modulate Treg function and to optimize Treg-based cell therapies for clinical translation.

ES-cell derived hematopoietic cells induce transplantation tolerance

Background

Bone marrow cells induce stable mixed chimerism under appropriate conditioning of the host, mediating the induction of transplantation tolerance. However, their strong immunogenicity precludes routine use in clinical transplantation due to the need for harsh preconditioning and the requirement for toxic immunosuppression to prevent rejection and graft-versus-host disease. Alternatively, embryonic stem (ES) cells have emerged as a potential source of less immunogenic hematopoietic progenitor cells (HPCs). Up till now, however, it has been difficult to generate stable hematopoietic cells from ES cells.

Methodology/Principal Findings

Here, we derived CD45⁺ HPCs from HOXB4-transduced ES cells and showed that they poorly express MHC antigens. This property allowed their long-term engraftment in sublethally irradiated recipients across MHC barriers without the need for immunosuppressive agents. Although donor cells declined in peripheral blood over 2 months, low level chimerism was maintained in the bone marrow of these mice over 100 days. More importantly, chimeric animals were protected from rejection of donor-type cardiac allografts.

Conclusions

Our data show, for the first time, the efficacy of ES-derived CD45⁺ HPCs to engraft in allogenic recipients without the use of immunosuppressive agents, there by protecting cardiac allografts from rejection.

FOXP3 expression in human kidney transplant biopsies is associated with rejection and time post transplant but not with favorable outcomes

Expression of the transcription factor forkhead box P3 (FOXP3) in transplant biopsies is of interest due to its role in a population of regulatory T cells. We analyzed FOXP3 mRNA expression using RT-PCR in 83 renal transplant biopsies for cause in relationship to histopathology, clinical findings and expression of pathogenesis-based transcript sets assessed by microarrays. FOXP3 mRNA was higher in rejection (T-cell and antibody-mediated) than nonrejection. Surprisingly, some native kidney controls also expressed FOXP3 mRNA. Immunostaining for FOXP3 was consistent with RT-PCR, showing interstitial FOXP3+ lymphocytes, even in some native kidney controls. FOXP3 expression correlated with interstitial inflammation, tubulitis, interstitial fibrosis, tubular atrophy, C4d positivity, longer time posttransplant, younger donors, class II panel reactive antibody >20% and transcript sets reflecting inflammation and injury, but unlike these features was time dependent. In multivariate analysis, higher FOXP3 mRNA was independently associated with rejection, T-cell-associated transcripts, younger donor age and longer time posttransplant. FOXP3 expression did not correlate with favorable graft outcomes, even when the analysis was restricted to biopsies with rejection. Thus FOXP3 mRNA expression is a time-dependent feature of inflammatory infiltrates in renal tissue. We hypothesize that time-dependent entry of FOXP3-positive cells represents a mechanism for stabilizing inflammatory sites.

Characterization of naturally occurring CD4+CD25+ regulatory T cells in rhesus monkeys

BACKGROUND

Translational research in a relevant preclinical model is recommended before Treg-inducing protocols can be implemented in humans. We have characterized rhesus monkey CD25 cells phenotypically and functionally.

METHODS

The phenotype of CD4(+)CD25(high) cells was determined by FACS, focusing on established markers of mouse and human Treg cells. Percentages of cells positive for CD45RA, CD62L, and intracellular CTLA-4 and FOXP3 were compared between CD4(+)CD25(high) and CD4(+)CD25(-) cells. CD25 cells stimulated with anti-CD3, ConA, and/or allogeneic peripheral blood mononuclear cells were mixed with freshly isolated CD25 cells. The suppressive activity of the CD25 cells in vitro was assessed using several experimental conditions.

RESULTS

Rhesus monkey CD4(+)CD25(high) cells expressed high intracellular levels of CTLA-4 and FOXP3, whereas expression was negligible in CD4(+)CD25(-) cells. The CD25(high) population was mostly CD45RA(-), indicative of a memory phenotype. The CD25(+) cells were anergic, because they showed low proliferative responses, no interleukin-2 production, and some interferon-gamma and interleukin-10 production. Proliferation of CD4(+)CD25(-) cells stimulated by anti-CD3 or allogeneic cells was decreased when CD4(+)CD25(-) cells were added at a 1:1 ratio. In addition, we found that CD25 cells inhibited the interleukin-2 and interferon-gamma production by anti-CD3-stimulated CD25 cells in a dose-dependent fashion, through a cell-cell contact-dependent mechanism.

CONCLUSIONS

Rhesus monkey CD4(+)CD25(+) cells have similar phenotypic and functional characteristics as natural Tregs in humans. These findings allow testing of Treg expansion and induction protocols in a relevant preclinical model, the rhesus monkey.