Pretransplant Immune‐Regulation Predicts Allograft Tolerance

CD4⁺ Tregs specific for noninherited maternal antigens (NIMA^d) are detectable in some but not all B6 × BDF₁ backcross, H‐2^b homozygous offspring, and their presence is strongly correlated with extent of maternal (BDF₁) microchimerism. We hypothesized that the level of pretransplant donor antigen‐specific Tregs could predict allograft tolerance. To test this idea, mice were screened for bystander suppression in a DTH assay, followed 1 week later by DBA/2 heterotopic heart transplantation. NIMA^d‐exposed, H‐2^b offspring that failed to suppress DTH uniformly rejected heart allografts (12/12) by d15. In contrast, 5/6 NIMA^d‐exposed DTH ‘regulators’ accepted their allografts >100 days. The defect in ‘nonregulator“ offspring could be corrected by transfer of CD4⁺CD25⁺, but not CD4⁺CD25^neg or CD8⁺T cells from transplant acceptor mice. In conclusion, donor‐specific T reg screening of F1 backcross offspring correctly predicted which recipients would accept a heart allograft. If translated to the clinic, similar pretransplant Treg screening could greatly enhance the effectiveness of tolerance as a clinical strategy in transplantation between family members.     

Role of IFNγ in Allograft Tolerance Mediated by CD4+CD25+ Regulatory T Cells by Induction of IDO in Endothelial Cells

Regulatory T cells have been described to specifically accumulate at the site of regulation together with effector T cells and antigen-presenting cells, establishing a state of local immune privilege. However the mechanisms of this interplay remain to be defined. We previously demonstrated, in a fully MHC mismatched rat cardiac allograft combination, that a short-term treatment with a deoxyspergualine analogue, LF15-0195, induces long-term allograft tolerance with a specific expansion of regulatory CD4+CD25+T cells that accumulate within the graft. In this study, we show that following transfer of regulatory CD4+T cells to a secondary irradiated recipient, regulatory CD25+Foxp3+ and CD25+Foxp3(-) CD4+T cells accumulate at the graft site and induce graft endothelial cell expression of Indoleamine 2, 3-dioxygenase (IDO) by an IFNgamma-dependent mechanism. Moreover, in vivo transfer of tolerance can be abrogated by blocking IFNgamma or IDO, and anti-IFNgamma reduces the survival/expansion of alloantigen-induced regulatory Foxp3+CD4+T cells. Together, our results demonstrate interrelated mechanisms between regulatory CD4+CD25+T cells and the graft endothelial cells in this local immune privilege, and a key role for IFNgamma and IDO in this process.     

Amnion‐Derived Multipotent Progenitor Cells Support Allograft Tolerance Induction

Donor‐specific immunological tolerance using high doses of bone marrow cells (BMCs) has been demonstrated in mixed chimerism‐based tolerance induction protocols; however, the development of graft versus host disease remains a risk. Here, we demonstrate that the co‐infusion of limited numbers of donor unfractionated BMCs with human amnion‐derived multipotent progenitor cells (AMPs) 7 days post–allograft transplantation facilitates macrochimerism induction and graft tolerance in a mouse skin transplantation model. AMPs + BMCs co‐infusion with minimal conditioning led to stable, mixed, multilineage lymphoid and myeloid macrochimerism, deletion of donor‐reactive T cells, expansion of CD4⁺CD25⁺Foxp3⁺ regulatory T cells (T_regs) and long‐term allograft survival (>300 days). Based on these findings, we speculate that AMPs maybe a pro‐tolerogenic cellular therapeutic that could have clinical efficacy for both solid organ and hematopoietic stem cell transplant applications.     

Mesenchymal Stem Cells Facilitate the Induction of Mixed Hematopoietic Chimerism and Islet Allograft Tolerance without GVHD in the Rat

Induction of hematopoietic chimerism and subsequent donor-specific immune tolerance via bone marrow transplantation is an ideal approach for islet transplantation to treat type-1 diabetes. We examined the potential of mesenchymal stem cells (MSCs) in the induction of chimerism and islet allograft tolerance without the incidence of graft-versus-host disease (GVHD). Streptozotocin-diabetic rats received a conditioning regimen consisting of antilymphocyte serum and 5 Gy total body irradiation, followed by an intraportal co-infusion of allogeneic MSCs, bone marrow cells (BMCs) and islets. Although all the recipients rejected the islets initially, half of them developed stable mixed chimerism and donor-specific immune tolerance, shown by the engraftment of donor skin and second-set islet transplants and acute rejection of a third-party skin. The engraftment of the primary islet allografts with stable chimerism was achieved by the addition of a 2-week peritransplant administration of 15-deoxyspergualin (DSG). Without MSCs, none of the recipients treated with DSG developed chimerism or reversal of diabetes. GVHD was not observed in any of the recipients infused with MSCs (0/15), whereas it occurred in 4/11 recipients without MSCs. These results indicate a potential use of MSCs for induction of hematopoietic chimerism and subsequent immune tolerance in clinical islet transplantation.     

Vascularized Osteomyocutaneous Allografts Are Permissive to Tolerance by Induction‐Based Immunomodulatory Therapy

Vascularized composite allografts (VCAs) are unique among transplanted organs in that they are composed of multiple tissues with disparate antigenic and immunologic properties. As the predominant indications for VCAs are non‐life‐threatening conditions, there is an immediate need to develop tolerance induction strategies and to elucidate the mechanisms of VCA rejection and tolerance using VCA‐specific animal models. In this study, we explore the effects of in vitro induced donor antigen‐specific CD4^?CD8^? double negative (DN) Treg‐based therapy, in a fully MHC mismatched mouse VCA such as a vascularized osteomyocutaneous as compared to a non‐VCA such as a full thickness skin (FTS) transplantation model to elucidate the unique features of VCA rejection and tolerance. We demonstrate that combined therapy with antigen‐induced CD4 derived DN Tregs and a short course of anti‐lymphocyte serum, rapamycin and IL‐2/Fc fusion protein results in donor‐specific tolerance to VCA, but not FTS allografts. Macrochimerism was detected in VCA but not FTS allograft recipients up to >60 days after transplantation. Moreover, a significant increase of CD4⁺Foxp3⁺ Tregs was found in the peripheral blood of tolerant VCA recipients. These data suggest that VCA are permissive to tolerance induced by DN Treg‐based induction therapy.

     

Superagonistic CD28 Antibody Induces Donor‐Specific Tolerance in Rat Renal Allografts

The ultimate goal of organ transplantation is to establish graft tolerance where CD4+CD25+FOXP3+ regulatory T (Treg) cells play an important role. We examined whether a superagonistic monoclonal antibody specific for CD28 (CD28 SA), which expands Treg cells in vivo, would prevent acute rejection and induce tolerance using our established rat acute renal allograft model (Wistar to Lewis). In the untreated or mouse IgG‐treated recipients, graft function significantly deteriorated with marked destruction of renal tissue, and all rats died by 13 days with severe azotemia. In contrast, 90% of recipients treated with CD28 SA survived over 100 days, and 70% survived with well‐preserved graft function until graft recovery at 180 days. Analysis by flow cytometry and immunohistochemistry demonstrated that CD28 SA induced marked infiltration of FOXP3+ Treg cells into the allografts. Furthermore, these long‐surviving recipients showed donor‐specific tolerance, accepting secondary (donor‐matched) Wistar cardiac allografts, but acutely rejecting third‐party BN allografts. We further demonstrated that adoptive transfer of CD4+CD25+ Treg cells, purified from CD28 SA‐treated Lewis rats, significantly prolonged allograft survival and succeeded in inducing donor‐specific tolerance. In conclusion, CD28 SA treatment successfully induces donor‐specific tolerance with the involvement of Treg cells, and thus the therapeutic value of this approach warrants further investigation and preclinical studies.     

Tolerance Induction or Sensitization in Mice Exposed to Noninherited Maternal Antigens (NIMA)

Developmental exposure to noninherited maternal antigens (NIMA) exerts a tolerizing or sensitizing influence on clinical transplantation in humans and experimental animals. The aim of this study was to determine if strain and gender differences influence the NIMA effect. Six different mouse strain backcross matings of F₁ females with homozygous males (‘NIMA backcross’) and corresponding control breedings of F1 males with homozygous females were performed. H‐2 homozygous offspring underwent heterotopic heart transplantation from fully allogeneic donors expressing noninherited H‐2 antigens. A NIMA tolerizing effect on heart allograft outcome was found in three of six breeding models. In all three cases, the tolerizing antigens were from an H‐2^d+ strain. The tolerogenic effect was greatest in male as compared with female recipients. Offspring from the three breeding models in which no tolerance was seen, appeared to be sensitized based on poorer graft survival, or enhanced T‐ or B‐cell responses to the noninherited H‐2^{b or k} antigens. Significantly higher percentages of maternal antigen⁺ cells were found in the peripheral blood of tolerant versus nontolerant strains of backcross mice prior to transplant. Our findings imply that transplants are predisposed to tolerance or rejection due to recipient developmental history and immunogenetic background.     

Prevention of CD40-Triggered Dendritic Cell Maturation and Induction of T-Cell Hyporeactivity by Targeting of Janus Kinase 3

Pharmacological targeting of Janus kinase 3 (JAK3) has been employed successfully to control allograft rejection and graft-vs.-host disease (GVHD). Recent evidence suggests that in addition to its involvement in common-gamma chain (cgamma) signaling of cytokine receptors, JAK3 is also engaged in the CD40 signaling pathway of peripheral blood monocytes. In this study, we assessed the consequences of JAK3 inhibition during CD40-induced maturation of myeloid dendritic cells (DCs), and tested the impact thereof on the induction of T-cell alloreactivity. Dendritic cells triggering through CD40 induced JAK3 activity, the expression of costimulatory molecules, production of IL-12, and potent allogeneic stimulatory capacity. In contrast, JAK3 inhibition with the rationally designed JAK3 inhibitor WHI-P-154 prevented these effects arresting the DCs at an immature level. Interestingly, DCs exposed to the JAK3-inhibitor during CD40-ligation induced a state of hyporeactivity in alloreactive T cells that was reversible upon exogenous IL-2 supplementation to secondary cultures. These results suggest that immunosuppressive therapies targeting the tyrosine kinase JAK3 may also affect the function of myeloid cells. This property of JAK3 inhibitors therefore represents a further level of interference, which together with the well-established suppression of cgamma signaling could be responsible for their clinical efficacy.     

Infusion of Mesenchymal Stem Cells and Rapamycin Synergize to Attenuate Alloimmune Responses and Promote Cardiac Allograft Tolerance

The inherent immunosuppressive properties and low immunogenicity of mesenchymal stems cells (MSCs) suggested their therapeutic potential in transplantation. We investigated whether MSCs could prolong allograft survival. Treatment involving infusion of MSCs into BALB/c recipients 24 hours after receiving a heart allograft from a C57BL/6 donor significantly abated rejection and doubled graft mean survival time compared to untreated recipients. Furthermore, combination therapy of MSCs and low-dose Rapamycin (Rapa) achieved long-term heart graft survival (>100 days) with normal histology. The treated recipients readily accepted donor skin grafts but rejected third-party skin grafts, indicating the establishment of tolerance. Tolerant recipients exhibited neither intragraft nor circulating antidonor antibodies, but demonstrated significantly high frequencies of both tolerogenic dendritic cells (Tol-DCs) and CD4⁺CD25⁺Foxp3⁺T cells in the spleens. Infusion of GFP⁺C57BL/6-MSCs in combination with Rapa revealed that the GFP-MSCs accumulated in the lymphoid organs and grafts of tolerant recipients. Thus, engraftment of infused MSCs within the recipient's lymphoid organs and allograft appeared to be instrumental in the induction of allograft-specific tolerance when administered in combination with a subtherapeutic dose of Rapamycin. This study supports the clinical applicability of MSCs in transplantation.     

Depletion of CD8 Memory T Cells for Induction of Tolerance of a Previously Transplanted Kidney Allograft

Heterologous immunologic memory has been considered a potent barrier to tolerance induction in primates. Induction of such tolerance for a previously transplanted organ may be more difficult, because specific memory cells can be induced and activated by a transplanted organ. In the current study, we attempted to induce tolerance to a previously transplanted kidney allograft in nonhuman primates. The conditioning regimen consisted of low dose total body irradiation, thymic irradiation, antithymocyte globulin, and anti‐CD154 antibody followed by a brief course of a calcineurin inhibitor. This regimen had been shown to induce mixed chimerism and allograft tolerance when kidney transplantation (KTx) and donor bone marrow transplantation (DBMT) were simultaneously performed. However, the same regimen failed to induce mixed chimerism when delayed DBMT was performed after KTx. We found that significant levels of memory T cells remained after conditioning, despite effective depletion of naïve T cells. By adding humanized anti‐CD8 monoclonal antibody (cM‐T807), CD8 memory T cells were effectively depleted and these recipients successfully achieved mixed chimerism and tolerance. The current studies provide ‘proof of principle’ that the mixed chimerism approach can induce renal allograft tolerance, even late after organ transplantation if memory T‐cell function is adequately controlled.     

Allergic Conjunctivitis Renders CD4+ T Cells Resistant to T Regulatory Cells and Exacerbates Corneal Allograft Rejection

Allergic diseases rob corneal allografts of immune privilege and increase immune rejection. Corneal allograft rejection in BALB/c allergic hosts was analyzed using a short ragweed (SWR) pollen model of allergic conjunctivitis. Allergic conjunctivitis did not induce exaggerated T‐cell responses to donor C57BL/6 (B6) alloantigens or stimulate cytotoxic T lymphocyte (CTL) responses. Allergic conjunctivitis did affect T regulatory cells (Tregs) that support graft survival. Exogenous IL‐4, but not IL‐5 or IL‐13, prevented Treg suppression of CD4⁺ effector T cells isolated from naïve mice. However, mice with allergic conjunctivitis developed Tregs that suppressed CD4⁺ effector T‐cell proliferation. In addition, IL‐4 did not inhibit Treg suppression of IL‐4Rα^?/? CD4⁺ T‐cell responses, suggesting that IL‐4 rendered effector T cells resistant to Tregs. SRW‐sensitized IL‐4Rα^?/? mice displayed the same 50% graft survival as nonallergic WT mice, that was significantly less than the 100% rejection that occurred in allergic WT hosts, supporting the role of IL‐4 in the abrogation of immune privilege. Moreover, exacerbation of corneal allograft rejection in allergic mice was reversed by administering anti‐IL‐4 antibody. Thus, allergy‐induced exacerbation of corneal graft rejection is due to the production of IL‐4, which renders effector T cells resistant to Treg suppression of alloimmune responses.     

Regulatory T Cells Are Critical to Tolerance Induction in Presensitized Mouse Transplant Recipients Through Targeting Memory T Cells

Memory T cells are a significant barrier to induction of transplant tolerance. However, reliable means to target alloreactive memory T cells have remained elusive. In this study, presensitization of BALB/c mice with C57BL/6 skin grafts generated a large number of OX40⁺CD44^hieffector/memory T cells and resulted in rapid rejection of donor heart allografts. Recognizing that anti‐OX40L monoclonal antibody (mAb) (α‐OX40L) monotherapy prolonged graft survival through inhibition and apoptosis of memory T cells in presensitized recipients, α‐OX40L was added to the combined treatment protocol of LF15–0195 (LF) and anti‐CD45RB (α‐CD45RB) mAb—a protocol that induced heart allograft tolerance in non‐presensitized recipients but failed to induce tolerance in presensitized recipients. Interestingly, this triple therapy restored donor‐specific heart allograft tolerance in our presensitized model that was associated with induction of tolerogenic dendritic cells and CD4⁺CD25⁺Foxp3⁺ T regulatory cells (Tregs). Of note, CD25⁺ T cell depletion in triple therapy recipients prevented establishment of allograft tolerance. In addition, adoptive transfer of donor‐primed effector/memory T cells into tolerant recipients markedly reduced levels of Tregs and broke tolerance. Our findings indicated that targeting memory T cells, by blocking OX40 costimulation in presensitized recipients was very important to expansion of Tregs, which proved critical to development of tolerance.     

CD4+CD25+调节性T细胞对小鼠肝脏移植自发性免疫耐受的影响

目的 研究CD4+CD25+调节性T细胞在诱导自发性肝脏免疫耐受中的作用.方法 向受体和供体注射抗CD25抗体(PC61)后进行小鼠原位肝脏移植,观测其生存时间.术后20～30 d切取移植肝脏行HE染色,同时观察CD4+CD25+T细胞对CD4+T细胞和CD8+T细胞功能的影响.结果 去除受体而不是供体小鼠的CD4+CD25+T细胞可以导致肝移植排斥反应.而且,去除CD4+CD25+T细胞使移植物的白细胞浸润明显增多,组织损伤加重.同时,去除CD4+CD25+T细胞导致CD4+T细胞的增殖活性和CD8+T细胞的细胞毒活性明显增强.结论 受体来源的CD4+CD25+调节性T细胞在小鼠肝脏移植免疫耐受诱导中起重要作用.

Abstract：

Objective To examine the contribution of CD4+ CD25+ regulatory T cells to liver transplant tolerance. Methods After injection of anti-CD25 monoclonal antibody (mAb, PC61), mouse orthotopic liver transplantation was performed and survivals were determined. The paraffin-embedded sections of hepatic allografts were cut and stained with hematoxylin and eosin (HE). Furthermore, the effect of CD4+ CD25+ regulatory T cells on proliferative response of CD4+ T cells and cytotoxicity of CD8+ T cells was examined by depleting these regulatory T cells. Results Depletion of these cells in the recipients but not in the donors before liver transplantation caused rejection. Histological analyses of hepatic allografts with PC61 treatment showed extensive leukocyte infiltration and tissue destruction, whereas those in the control group showed minimal changes. Moreover, elimination of CD4+CD25+ T cells resulted in the enhancement of both proliferative response of CD4+ T cells and cytotoxicity of CD8+ T cells against donor-type alloantigen. Conclusions These results suggest that CD4+CD25+ regulatory T cells were important for tolerance induction to hepatic allografts.     

CD4+ CD25bright+ Regulatory T Cells Can Mediate Donor Nonreactivity in Long-Term Immunosuppressed Kidney Allograft Patients

CD4+ CD25bright+ FoxP3+ T cells are potent regulators of T-cell reactivity, but their possible involvement in donor-specific nonresponsiveness after clinical kidney transplantation remains to be elucidated. We assessed the proliferative donor-reactivity in 33 kidney allograft recipients who were maintained on a combination of proliferation inhibitors (mycophenolate mofetil (MMF) or Azathioprine (Aza)) and prednisone, long (> 5 years) after transplantation. Of the 33 patients, 8 still exhibited donor-reactivity, whereas 25 were classified as donor nonreactive patients. Within these 25 donor nonreactive patients, we assessed the involvement of CD4+ CD25bright+ regulatory T cells both by depleting them from the responder population as well as by reconstituting them to the CD25(-/dim) effector population. The absence of proliferation in these 25 patients, was abolished in 7 (28%) recipients upon depletion of the CD4+ CD25bright+ T cells. Reconstitution of these cells suppressed the donor-reactivity in a dose-dependent manner. Adding-back CD4+ CD25bright+ T cells inhibited the anti-third party response in all recipients, indicating that functional CD4+ CD25bright+ T cells circulate despite more then 5 years of immunosuppressive treatment. Altogether, we conclude that in long-term immunosuppressed kidney allograft patients functional regulatory CD4+ CD25bright+ T cells circulate but that these cells mediate donor non reactivity only in a subset of patients.     

Expression of CD39 by Human Peripheral Blood CD4+CD25+ T Cells Denotes a Regulatory Memory Phenotype

We have shown that CD39 and CD73 are coexpressed on the surface of murine CD4⁺Foxp3⁺ regulatory T cells (Treg) and generate extracellular adenosine, contributing to Treg immunosuppressive activity. We now describe that CD39, independently of CD73, is expressed by a subset of blood‐derived human CD4⁺CD25⁺CD127lo Treg, defined by robust expression of Foxp3. A further distinct population of CD4⁺CD39⁺ T lymphocytes can be identified, which do not express CD25 and FoxP3 and exhibit the memory effector cellular phenotype. Differential expression of CD25 and CD39 on circulating CD4⁺ T cells distinguishes between Treg and pathogenic cellular populations that secrete proinflammatory cytokines such as IFNγ and IL‐17. These latter cell populations are increased, with a concomitant decrease in the CD4⁺CD25⁺CD39⁺ Tregs, in the peripheral blood of patients with renal allograft rejection. We conclude that the ectonucleotidase CD39 is a useful and dynamic lymphocytes surface marker that can be used to identify different peripheral blood T cell‐populations to allow tracking of these in health and disease, as in renal allograft rejection.     

Donor‐Specific CD8+Foxp3+ T Cells Protect Skin Allografts and Facilitate Induction of Conventional CD4+Foxp3+ Regulatory T Cells

CD4⁺ regulatory T cells play a critical role in tolerance induction in transplantation. CD8⁺ suppressor T cells have also been shown to control alloimmune responses in preclinical and clinical models. However, the exact nature of the CD8⁺ suppressor T cells, their induction and mechanism of function in allogeneic transplantation remain elusive. In this study, we show that functionally suppressive, alloantigen‐specific CD8⁺Foxp3⁺ T cells can be induced and significantly expanded by stimulating naïve CD8⁺ T cells with donor dendritic cells in the presence of IL‐2, TGF‐β1 and retinoic acid. These CD8⁺Foxp3⁺ T cells express enhanced levels of CTLA‐4, CCR4 and CD103, inhibit the up‐regulation of costimulatory molecules on dendritic cells, and suppress CD4 and CD8 T cell proliferation and cytokine production in a donor‐specific and contact‐dependent manner. Importantly, upon adoptive transfer, the induced CD8⁺Foxp3⁺ T cells protect full MHC‐mismatched skin allografts. In vivo, the CD8⁺Foxp3⁺ T cells preferentially traffic to the graft draining lymph node where they induce conventional CD4⁺Foxp3⁺ T cells and concurrently suppress effector T cell expansion. We conclude that donor‐specific CD8⁺Foxp3⁺ suppressor T cells can be induced and exploited as an effective form of cell therapy for graft protection in transplantation.     

Anti‐TCRβ mAb Induces Long‐Term Allograft Survival by Reducing Antigen‐Reactive T Cells and Sparing Regulatory T Cells

TCR specific antibodies may modulate the TCR engagement with antigen–MHC complexes, and in turn regulate in vivo T cell responses to alloantigens. Herein, we found that in vivo administration of mAbs specific for mouse TCRβ (H57–597), TCRα or CD3 promptly reduced the number of CD4⁺ and CD8⁺ T cells in normal mice, but H57–597 mAb most potently increased the frequency of CD4⁺Foxp3⁺ Treg cells. When mice were injected with staphylococcal enterotoxin B (SEB) superantigen and H57–597 mAb, the expansion of SEB‐reactive Vβ8⁺ T cells was completely abrogated while SEB‐nonreactive Vβ2⁺ T cells remained unaffected. More importantly, transient H57–597 mAb treatment exerted long‐lasting effect in preventing T cell responses to alloantigens, and produced long‐term cardiac allograft survival (>100 days) in 10 out of 11 recipients. While Treg cells were involved in maintaining donor‐specific long‐term graft survival, T cell homeostasis recovered over time and immunity was retained against third party allografts. Moreover, transient H57–597 mAb treatment significantly prolonged survival of skin allografts in naïve recipients as well as heart allografts in skin‐sensitized recipients. Thus, transient modulation of the TCRβ chain by H57–597 mAb exhibits potent, long‐lasting therapeutic effects to control alloimmune responses.