Idd loci synergize to prolong islet allograft survival induced by costimulation blockade in NOD mice

OBJECTIVE—NOD mice model human type 1 diabetes and are used to investigate tolerance induction protocols for islet transplantation in a setting of autoimmunity. However, costimulation blockade–based tolerance protocols have failed in prolonging islet allograft survival in NOD mice.RESEARCH DESIGN AND METHODS—To investigate the underlying mechanisms, we studied the ability of costimulation blockade to prolong islet allograft survival in congenic NOD mice bearing insulin-dependent diabetes (Idd) loci that reduce the frequency of diabetes.RESULTS—The frequency of diabetes is reduced in NOD.B6 Idd3 mice and is virtually absent in NOD.B6/B10 Idd3 Idd5 mice. Islet allograft survival in NOD.B6 Idd3 mice treated with costimulation blockade is prolonged compared with NOD mice, and in NOD.B6/B10 Idd3 Idd5, mice islet allograft survival is similar to that achieved in C57BL/6 mice. Conversely, some Idd loci were not beneficial for the induction of transplantation tolerance. Alloreactive CD8 T-cell depletion in (NOD × CBA)F1 mice treated with costimulation blockade was impaired compared with similarly treated (C57BL/6.H2^g7 × CBA)F1 mice. Injection of exogenous interleukin (IL)-2 into NOD mice treated with costimulation prolonged islet allograft survival. NOD.B6 Idd3 mice treated with costimulation blockade deleted alloreactive CD8 T-cells and exhibited prolonged islet allograft survival.CONCLUSIONS—Il2 is the Idd3 diabetes susceptibility gene and can influence the outcome of T-cell deletion and islet allograft survival in mice treated with costimulation blockade. These data suggest that Idd loci can facilitate induction of transplantation tolerance by costimulation blockade and that IL-2/Idd3 is a critical component in this process.The NOD mouse is a model of type 1–like autoimmune diabetes and is used to study costimulation blockade–based transplantation tolerance within the context of autoimmunity (1–4). However, costimulation blockade protocols fail in NOD mice. To investigate further the cellular and genetic control of costimulation blockade–induced transplantation tolerance, we used NOD Idd congenic mice that have small introgressed regions of genetic intervals derived from diabetes-resistant C57 stocks. These mice exhibit varying degrees of protection from autoantibodies, insulitis, and diabetes (5). Using Idd congenic NOD mice, we have observed that islet allograft survival is improved by the addition of the diabetes-protective Idd3 locus (6,7).Idd3 modulates infiltration of autoreactive lymphocytes into the islets (8), and there is compelling evidence that Idd3 is the interleukin (IL)-2 gene (9). In vivo stimulated NOD T-cells produce twofold less IL-2 mRNA than cells from NOD congenic mice having protective alleles at Idd3 (9,10). Neutralizing antibodies to IL-2 lead to accelerated disease in NOD mice (11), and targeted genetic disruption of IL-2 accelerates type 1–like autoimmune diabetes (9). Treatment with exogenous IL-2 inhibits diabetes development in NOD mice and improves T regulatory (Treg) function (12). IL-2 is also known to have a nonredundant role in CD8 T-cell activation–induced cell death via the CD95 (Fas) pathway (13), is required for the development of self-tolerance (14), and is essential for the induction of allograft tolerance by costimulation blockade (15). However, IL-2 is a double-edged sword, since administration of IL-2 in vivo can either enhance or depress a cytotoxic T lymphocyte (CTL) response (16).In this study, we show that costimulation blockade fails to delete alloreactive CD8 T-cells in NOD mice. Genetic replacement of IL-2 in NOD.B6 Idd3 mice enhances alloreactive CD8 T-cell deletion and improves islet allograft survival. Finally, we show that Idd3 synergizes with genes within the Idd5 interval, leading to permanent islet allograft survival in a majority of NOD.B6/B10 Idd3 Idd5 mice treated with costimulation blockade.     

Pancreatic islet xenograft tolerance after short-term costimulation blockade is associated with increased CD4+ T cell apoptosis but not immune deviation

BACKGROUND: Our purpose was to determine if short-term inhibition of the CD40/CD40L and CD28/B7 costimulatory pathways was capable of inducing specific unresponsiveness to pancreatic islet xenografts and to ascertain the mechanism of tolerance induction. METHODS: Diabetic B6AF1 mice were transplanted with Wistar or DA rat islets and were treated short term with CTLA4-Fc and anti-CD40L mAb (MR1). RESULTS: Coadministration of CTLA4-Fc with MR1, resulted in indefinite rat islet xenograft survival in mice. Tolerance was species but not strain specific as long-term surviving recipients rejected third party BALB/c islet allografts but accepted a second rat islet xenograft from the same or different donor strain. Tolerance induction was associated with a large leukocyte infiltrate that did not exhibit features of immune deviation as intragraft T cell-specific cytokine gene expression was globally reduced. In particular, interleukin-4 gene expression was markedly suppressed. There was a complete inhibition of anti-donor IgG, IgG1, and IgM antibody in the serum of CTLA4-Fc/MR1- treated animals. Tolerance induction was associated with increased CD4+ T cell apoptosis as there was an increased proportion of annexin-V staining and Fas expressing CD4+ T cells and a decrease in CD4+ T cell Bcl-2 expression in the grafts and draining lymph nodes of CTLA4-Fc/MR1-treated recipients. CONCLUSION: Combined costimulatory blockade was capable of producing tolerance to pancreatic islet xenografts. The induction of this tolerant state was associated with increased T cell apoptosis, whereas the maintenance phase of tolerance was associated with the accumulation of a large number of inactive lymphocytes within the graft.     

Islet allograft survival induced by costimulation blockade in NOD mice is controlled by allelic variants of Idd3

NOD mice develop type 1 autoimmune diabetes and exhibit genetically dominant resistance to transplantation tolerance induction. These two phenotypes are genetically separable. Costimulation blockade fails to prolong skin allograft survival in (NOD x C57BL/6)F1 mice and in NOD-related strains made diabetes-resistant by congenic introduction of protective major histocompatibility complex (MHC) or non-MHC Idd region genes. Here, we tested the hypothesis that the genetic basis for the resistance of NOD mice to skin allograft tolerance also applies to islet allografts. Surprisingly, costimulation blockade induced permanent islet allograft survival in (NOD x C57BL/6)F1 mice but not in NOD mice. After costimulation blockade, islet allograft survival was prolonged in diabetes-resistant NOD.B6 Idd3 mice and shortened in diabetes-free C57BL/6 mice congenic for the NOD Idd3 variant. Islet allograft tolerance could not be induced in diabetes-resistant NOD.B10 Idd5 and NOD.B10 Idd9 mice. The data demonstrate that 1) NOD mice resist islet allograft tolerance induction; 2) unlike skin allografts, resistance to islet allograft tolerance is a genetically recessive trait; 3) an Idd3 region gene(s) is an important determinant of islet allograft tolerance induction; and 4) there may be overlap in the mechanism by which the Idd3 resistance locus improves self-tolerance and the induction of allotolerance.     

Prolonged islet graft survival in NOD mice by blockade of the CD40-CD154 pathway of T-cell costimulation

Allorejection and recurrence of autoimmunity are the major barriers to transplantation of islets of Langerhans for the cure of type 1 diabetes in humans. CD40-CD154 (CD40 ligand) interaction blockade by the use of anti-CD154 monoclonal antibody (mAb) has shown efficacy in preventing allorejection in several models of organ and cell transplantation. Here we report the beneficial effect of the chronic administration of a hamster anti-murine CD154 mAb, MR1, in prolonging islet graft survival in NOD mice. We explored the transplantation of C57BL/6 islets into spontaneously diabetic NOD mice, a combination in which both allogeneic and autoimmune components are implicated in graft loss. Recipients were treated either with an irrelevant control antibody or with MR1. MR1 administration was effective in prolonging allograft survival, but did not provide permanent protection from diabetes recurrence. The autoimmune component of graft loss was studied in spontaneously diabetic NOD mice that received syngeneic islets from young male NOD mice. In this combination, a less dramatic yet substantial delay in diabetes recurrence was observed in the MR1-treated recipients when compared with the control group. Finally, the allogeneic component was explored by transplanting C57BL/6 islets into chemically induced diabetic male NOD mice. In this setting, long-term graft survival (>100 days) was achieved in MR1-treated mice, whereas control recipients rejected their grafts within 25 days. In conclusion, chronic blockade of CD154 results in permanent protection from allorejection and significantly delays recurrence of diabetes in NOD mice.     

Prolongation of islet allograft survival by coexpression of CTLA4Ig and CD40LIg in mice

BACKGROUND: B7/CD28 and CD40/CD40L have been well established as important costimulatory pathways. Cytotoxic T lymphocyte-associated antigen-4 (CTLA4) delivers negative signals to antigen-presenting cells to down-regulate proinflammatory responses and competitively inhibits the binding of B7 and CD28. Signals from the CD40/CD40L costimulatory pathway also play an important role in acute rejection of organ grafts. METHODS: Recombinant adenoviruses Ad-sCD40LIg-IRES2-CTLA4Ig, Ad-CTLA4Ig, and Ad-sCD40LIg were constructed to express sCD40LIg and CTLA4Ig simultaneously or separately as described previously. Streptozocin-induced diabetic BALB/c mice were injected with recombinant adenovirus, receiving approximately 500 donor islets isolated from C57BL/6 mice under the left kidney capsule. Five groups were assigned according to the treatment: nontreated group, Ad-Shuttle-CMV-treated group, Ad-CTLA4Ig-treated group, Ad-sCD40LIg-treated group, and Ad-sCD40LIg-IRES2-CTLA4Ig-treated group. The islet graft mean survival time (MST) was evaluated in the present study. RESULTS: Compared to the islet graft MST of the nontreated group (7.3+/-0.82 days) or Ad-Shuttle-CMV-treated group (7.2+/-1.47 days), the Ad-CTLA4Ig-treated and Ad-CD40LIg-treated islet graft survivals in recipients were 56.3+/-13.71 days (P<.01) and 47.3+/-15.64 days (P<.05), respectively. The islet graft MST was dramatically prolonged to 116.3+/-20.32 days in the Ad-sCD40LIg-IRES2-CTLA4Ig-treated group (P<.01). CONCLUSION: Simultaneous blockade of the CD40/CD40L and B7/CD28 costimulatory pathways via coexpression of sCD40LIg and CTLA4Ig mediated by replication-defective adenovirus may be an acceptable method to induce immune tolerance.     

Mediation of skin allograft rejection in scid mice by CD4+ and CD8+ T cells.

We analyzed the role of CD4+ and CD8+ T cells in H-2-disparate skin allograft rejection in the mutant mouse strain C.B-17/Icr scid with severe combined immunodeficiency. On the day of skin allografting, scid mice were adoptively transferred with negatively selected CD4+ or CD8+ splenocytes from normal unsensitized C.B-17/Icr mice. These populations were obtained using a double-mAb--plus--complement elimination protocol using anti-CD4 or anti-CD8 mAb that resulted in no detectable CD4+ or CD8+ cells by FACS and negligible numbers of cytolytic T lymphocytes by limiting dilution analysis in anti-CD8 treated populations. Spleen cells were removed from grafted mice at the time of rejection and were tested in vitro for antidonor reactivity in several assays: mixed lymphocyte culture, cell-mediated lympholysis, and LDA for CTL and for IL-2-producing HTL. The presence of Thy 1.2+, CD4+, or CD8+ cells was determined by FACS. All control C.B-17 mice and scid mice adoptively transferred with nondepleted CD4+, and CD8+ cells rejected skin allografts with similar mean survival times (15.6 +/- 1.5, 18.8 +/- 3.4, 18.0 +/- 5.4, respectively), whereas control scid mice retain skin allografts indefinitely (all greater than 100 days). C.B-17 syngeneic grafts survived indefinitely in all groups. At the time of rejection, splenocytes from scid mice receiving CD4+ cells had negligible donor-specific cytotoxicity in CML and negligible numbers of CTL by LDA, but demonstrated a good proliferative response in MLC and IL-2-producing cells by LDA (frequency = 1/1764). There were no detectable CD8+ cells present by FACS analysis. Conversely, splenocytes from scid mice adoptively transferred with CD8+ cells had strong donor-specific cytotoxicity in CML (58.8% +/- 16.1%) and CTL by LDA (frequency = 1/3448), but no significant proliferation was detected in MLC. There were no detectable CD4+ cells by FACS, but there were small numbers of IL-2-producing cells by LDA (frequency = 1/10,204). These data demonstrate that CD4+ cells adoptively transferred into scid mice are capable of mediating skin allograft rejection in the absence of any detectable CD8+ cells or significant functional cytolytic activity. The adoptive transfer of CD8+ cells also results in skin allograft rejection in the absence of detectable CD4+ cells. The detection of small numbers of IL-2 secreting cells in these mice may indicate that CD(8+)-mediated allograft rejection in this model is dependent on IL-2-secreting CD8+ cells.     

Prolonged islet allograft survival in diabetic NOD mice by targeting CD45RB and CD154

Clinical islet transplantation is a successful procedure that can improve the quality of life in recipients with diabetes. A drawback of the procedure is the need for chronic administration of immunosuppressive drugs that, among other side effects, are potentially diabetogenic. Definition of immunosuppressive protocols that utilize nondiabetogenic compounds could further improve islet transplantation outcome. We used the NOD mouse to assess the effect of targeting the T-lymphocyte surface receptors CD45RB and CD154 in preventing loss of allogeneic islet grafts as a result of recurrence of autoimmunity and allorejection. Administration of the two antibodies led to significantly prolonged allograft survival, with a percentage of grafts surviving long-term. The therapeutic efficacy of the treatment was paralleled by a shift in CD45RB isoform expression on T-lymphocytes, increased in vitro responsiveness to interleukin-7, and increased in vitro gamma-interferon production after anti-CD3 antibody stimulation. Furthermore, graft infiltration by CD8+ T-cells was remarkably reduced. Recipient mice bearing functioning allografts were otherwise immunocompetent, as assessed in vivo and in vitro by numerous tests, including intragraft cytokine production, responsiveness to polyclonal stimulation and alloantigens, and analysis of cell subset phenotype. These data show that nondiabetogenic regimens of immunomodulation can lead to prolonged islet allograft survival in the challenging NOD mouse model.     

阻断OX40和CD40协同共刺激信号延长小鼠胰岛移植物存活时间

目的 研究阻断OX40/OX40L和CD40/CD154L协同共刺激通路对小鼠胰岛移植物存活的影响及其机制.方法 以DBA/2小鼠为供者,C57BL/6小鼠为受者,制作胰岛移植模型.受鼠分为4组.(1)对照组,注射IgG; (2)抗OX40组,注射抗OX40L单克隆抗体;(3)抗CD154组,注射抗CD154单克隆抗体;(4)联合治疗组,注射抗OX40L单克隆抗体和抗CD1 54单克隆抗体.记录各组胰岛移植物平均存活时间(MST).将CD154敲除小鼠处死,取其脾脏T淋巴细胞,体外检测活化T淋巴细胞表面OX40的表达;在活化T淋巴细胞中加入不同浓度的抗OX40L单克隆抗体,体外检测T淋巴细胞增殖情况.结果 对照组胰岛移植物MST为19 d,抗CD154组胰岛移植物MST为48 d(P＜0.05);抗OX40组胰岛移植物MST为22 d,与前两组相比较,差异无统计学意义(P＞0.05);联合治疗组胰岛移植物MST＞ 150 d,高于另外3组(P＜0.05).66％的胞表达OX40,较初始T淋巴细胞的表达率高(2％,P＜0.05);加入抗OX40L单克隆抗体后,T淋巴细胞增殖受抑制且呈剂量依赖性.结论 阻断OX40/OX40L和CD40/CD154L双通路可诱导小鼠胰岛移植物长期存活, 其发挥作用的关键机制是抑制了T淋巴细胞的增殖.     

Bcl-2 protection of islet allografts is unmasked by costimulation blockade

One major limitation in pancreatic islet transplantation is availability of donor tissue. Donor shortage is exacerbated by islet apoptosis from the stresses of islet isolation and transplantation. Furthermore, the side effects of immunosuppressive drugs preclude transplants into patients whose diabetes is controlled by parenteral insulin. We hypothesised that over-expressing anti-apoptotic Bcl-2 or secretion of immunomodulatory CTLA4Ig molecules in islet beta cells would enhance survival of transplanted islets while minimizing systemic side effects. Over-expression of Bcl-2 neither significantly increased preservation of islet cell mass after transplantation into immunocompromised recipients nor decreased cytokine-mediated apoptosis in vitro. Although Bcl-2 over-expression alone was insufficient in protecting islet allografts from rejection, its beneficence was shown by the enhancement of protection when the adaptive immune response was inhibited by locally produced CTLA4Ig. Thus, the combination of anti-apoptotic and immunosuppressive intervention has additive or synergistic efficacy and may reduce the level of systemic immunosuppression or quantity of donor tissue required.     

The role of CD8+ and CD4+ cells in islet allograft rejection

The requirements of CD8+ and CD4+ cells for islet graft rejection in combinations with different histoincompatibilities were investigated by in vivo administration of anti-Lyt-2.2 (CD8) mAb, anti-L3T4 (CD4) mAb, or both to recipient mice. In B10.AQR----B10.A (H-2K-incompatible) and B10.A(5R)----B10.A (H-2K- and IA-incompatible) combinations, administration of either anti-Lyt-2.2 (CD8) or anti-L3T4 (CD4) mAb completely blocked islet graft rejection, indicating that neither CD8+ cells nor CD4+ cells alone were capable of mediating rejection, and that collaboration of CD8+ cells and CD4+ cells was necessary. On the other hand, in the BALB/c----B6 (H-2- and non-H-2-incompatible) combination, administration of anti-Lyt-2.2 (CD8) or anti-L3T4 (CD4) mAb resulted in rejection of most of the grafts, although survival was prolonged significantly, and administration of both anti-Lyt-2.2 (CD8) and anti-L3T4 (CD4) mAb together completely blocked rejection. These results suggested that either CD8+ or CD4+ cells were capable of mediating rejection, but that rejection was maximal in the presence of both T cell subsets. Immunohistochemical analyses showed marked depletion of CD8+ cells and CD4+ cells in grafted islets as well as spleens when anti-Lyt-2.2 (CD8) and anti-L3T4 (CD4) mAb, respectively, were injected.     

Prolonged limb allograft survival with CD 40 costimulation blockade, T-cell depletion, and megadose donor bone-marrow transfusion

The purpose of this study was to determine the efficacy of a treatment regimen consisting of CD 40 costimulation blockade, T-cell depletion, and megadose donor bone marrow transfusion in the limb allograft model. C57Bl/6 mice underwent limb transplantation from Balb/c mice and received MR1 (anti-CD 40 ligand monoclonal antibody), and CD4(+) and CD8(+) T cell-depleting antibodies with and without 120 x 10(6) donor bone-marrow transfusion. Recipients treated only with antibodies showed rejection at 51.4+/-17 (mean+/-SEM) days, while those who also received donor bone marrow had allograft survival of 67+/-16.4 days, with a range up to 91 days. Treated specimens with rejection had less lymphocytic infiltration than untreated controls. Recipients of donor bone marrow also demonstrated early mixed chimerism, which disappeared after 1 month. While allograft survival was prolonged, tolerance was not achieved, and the mechanism of rejection was more consistent with a chronic process.     

Rat xenograft survival in mice treated with donor-specific transfusion and anti-CD154 antibody is enhanced by elimination of host CD4+ cells

BACKGROUND: Treatment with a donor-specific transfusion (DST) and a brief course of anti-mouse CD154 (anti-CD40-ligand) monoclonal antibody (mAb) prolongs the survival of both allografts and rat xenografts in mice. The mechanism by which allograft survival is prolonged is incompletely understood, but depends in part on the presence of CD4+ cells and the deletion of alloreactive CD8+ T cells. Less is known about the mechanism by which this protocol prolongs xenograft survival. METHODS: We measured rat islet and skin xenograft survival in euthymic and thymectomized mice treated with combinations of DST, anti-CD154 mAb, anti-CD4 mAb, and anti-CD8 mAb. Recipients included C57BL/6, C57BL/6-scid, C57BL/6-CD4null, and C57BL/6-CD8null mice. RESULTS: Pretreatment with a depleting anti-CD4 mAb markedly prolonged the survival of both skin and islet xenografts in mice given DST plus anti-CD154 mAb. Comparable prolongation of xenograft survival was obtained in C57BL/6-CD4null recipients treated with DST and anti-CD154 mAb. In contrast, anti-CD8 mAb did not prolong the survival of either islet or skin xenografts in mice treated with DST and anti-CD154 mAb. Thymectomy did not influence xenograft survival in any treatment group. Adoptive transfer of splenocytes from C57BL/6-CD4null recipients treated with DST and anti-CD154 mAb and bearing long-term skin xenografts revealed the presence of residual xenoreactive cells. CONCLUSIONS: These data suggest that treatment with DST and anti-CD154 mAb induces a state of "functional" transplantation tolerance. They also support the hypothesis that both the induction and maintenance of graft survival based on this protocol depend on different cellular mechanisms in allogeneic and xenogeneic model systems.     

Indefinite mouse heart allograft survival in recipient treated with CD4+CD25+ regulatory T cells with indirect allospecificity and short term immunosuppression

CD4⁺CD25⁺ regulatory T cells (Tregs) play a crucial role in controlling immune responses. It is an appealing strategy to harness Tregs for adoptive cell therapy to induce tolerance to allografts. Several approaches have been developed to expand antigen-specific Tregs. Despite the large body of experimental data from murine studies demonstrating the great potential of these cells for clinical application, Treg adoptive transfer therapy was used in immunodeficient animals or in strain combinations with limited histiocompatibility. The aim of this study was to investigate whether Treg lines can protect from allograft rejection in a fully MHC-mismatched strain combination and whether the presence of Tregs with indirect allospecificity offered an advantage compared to self-reactive Tregs. Treg lines with self-specificity or with indirect allospecificity were generated by stimulating BL/6 CD4⁺CD25⁺ T cells with autologous immature DCs either unpulsed or pulsed with K^d peptide. The Treg lines were injected into recipient mice in combination with temporary depletion of CD8⁺ T cells and a short course of Rapamycin. The data demonstrate that Treg lines with indirect allospecificity can be generated and most importantly they can induce indefinite survival of BALB/c hearts transplanted into BL/6 recipients when combined with short term immunosuppression. However, the Treg lines with self-specificity were only slightly less effective. The data presented in this study demonstrate the potential of ex vivo expanded Treg lines for adoptive cell therapy to promote transplantation tolerance.     

Role of CD4+ and CD8+ T cells in murine skin and heart allograft rejection across different antigenic desparities

The factors that influence the relative contribution of the T cell subsets to allograft rejection remain unclear. We compared skin and heart rejection in CD4 Knockout (KO), and CD8 KO mice across full-, minor-, and class II histocompatibility antigen (HA) mismatches. Skin allografts were rejected by either CD4+ or CD8+ T cells alone at any degree of antigenic mismatch. However, either the absence of CD4+ cells or a lesser degree of HA mismatch resulted in prolongation of graft survival. In contrast, fully allogeneic heart grafts were accepted in CD4 KO recipients, and minor HA mismatched heart grafts were accepted by both CD4 KO and CD8 KO mice. Thus, the T cell subsets required for allograft rejection are determined by the immunogenicity of the tissue transplanted. In the absence of CD8+ T cells, perforin and Fas ligand (FasL) but not granzyme B mRNA were detected in rejecting grafts. Thus, granzyme B is a CD8+ cytotoxic T lymphocyte (CTL)-specific effector molecule.     

Long-term islet allograft survival in nonobese diabetic mice treated with tacrolimus,rapamycin, and anti-interleukin-2 antibody

BACKGROUND: Nonobese diabetic (NOD) mice develop autoimmune diabetes with features similar to those observed in the human disease. The concurrence of allorecognition and recurrence of autoimmunity might explain why most of the treatments successful in preventing islet allograft destruction in other nonautoimmune combinations often fail in NOD recipients. To assess the value of the NOD mouse model for the evaluation of treatments relevant to clinical islet transplantation, the authors have tested the effect of a protocol closely resembling the one successfully used in the Edmonton clinical trial on the survival of islet allografts in NOD mice. METHODS: C57BL/6 islets were transplanted under the kidney capsule of spontaneously diabetic NOD mice. Treatment consisted of a combination of rapamycin, tacrolimus, and anti-interleukin (IL)-2 monoclonal antibody. Control groups received each treatment alone, a combination of two agents, or no treatment. RESULTS: Untreated animals invariably lost their graft within 13 days. Administration of rapamycin and tacrolimus significantly prolonged graft survival, with two of seven animals bearing a functional graft longer than 100 days. Addition of anti-IL-2 antibody therapy further improved graft survival, with six of eight grafts functioning longer than 100 days and two of eight grafts functioning longer than 200 days. CONCLUSIONS: In view of the limited success obtained with other treatments in this model, the dramatic prolongation of graft survival observed in the authors' study, by using a therapy that mimics one successfully used in clinical trials, seems to validate the NOD mouse as a meaningful model for the study of therapeutic interventions for the prevention of islet graft loss.     

Control of intestinal allograft rejection by FTY720 and costimulation blockade

INTRODUCTION: The clinical application of small bowel transplantation (SBTx) is hampered by its pronounced immunogenicity. In this study we examined the effects of the novel immunosuppressant FTY720 and costimulation blockade by an anti-CD40L mAb (MR-1) in a stringent mouse model of SBTx. METHODS: SBTx was performed in mice with a full MHC mismatch (donors: C3H=H-2(k); recipients: C57BL/6=H-2(b)). Recipients were divided into four groups: 1, untreated group; 2, MR1 monotherapy (500 microg IV on days 0, 2, 4, and 7); 3, FTY720 monotherapy (1 mg/kg body weight PO for 14 consecutive days after transplantation); 4, FTY720 plus MR1-treated group. Graft rejection grades were assessed by H&E staining. Graft mesenteric lymph nodes (MLNs), Peyer's patches (PPs), as well as intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs) were analyzed by flow cytometry and three-color immunofluorescence staining. RESULTS: Neither FTY720 nor MR1 monotherapy was efficient in preventing the rejection of mouse intestinal allografts, whereas FTY720 plus MR1 profoundly inhibited the rejection response at the 14th posttransplant day. The infiltration of host lymphocytes was reduced in graft MLNs, PPs, IELs, and LPLs by FTY720 therapy. FTY720 plus MR1 inhibited host CD8(+) T-cell infiltration in graft LPLs when compared with grafts treated with FTY720 only. Additionally, two subpopulations, CD11b(+high) Gr1(-) and CD11b(+intermediate) Gr1(+) cells, were decreased in FTY720-treated grafts. CONCLUSIONS: FTY720 plus MR1 efficiently delayed intestinal allograft rejection in a mouse model by preventing the infiltration of host lymphocytes, particularly of CD8(+) cells.     

Combined treatment with CD40 costimulation blockade, T-cell depletion, low-dose irradiation, and donor bone marrow transfusion in limb allograft survival

To determine the efficacy of a regimen based on CD40 costimulation blockade and donor bone marrow in the limb allograft model, C57Bl/6 mice received limb allografts from Balb/c mice and either no treatment or a combination of MR1 (anti-CD40 ligand monoclonal antibody), CD4+ and CD8+ T-cell-depleting antibodies, low-dose irradiation, and bone marrow transfusion from Balb/c donors for 1 or 2 weeks. Recipients treated for 1 week showed rejection at 38.2 +/- 5.4 (mean +/- SEM) days, while those treated for 2 weeks had allograft survival of 56.5 +/- 9.9, with a range up to 91 days. Histology demonstrated rejection which was less cell-mediated and suggestive of transplant vasculopathy. Differential rejection of skin occurred first. Thus, a combined regimen based on CD40 costimulatory blockade and donor marrow significantly prolonged allograft survival. However, tolerance was not achieved, and histology suggests chronic rejection as a possible cause of allograft loss.