Combined Coinhibitory and Costimulatory Modulation with Anti-BTLA and CTLA4Ig Facilitates Tolerance in Murine Islet Allografts

Complex interactions between positive and negative cosignaling receptors ultimately determine the fate of the immune response. The recently identified coinhibitory receptor, B and T lymphocyte attenuator (BTLA), contributes to regulation of autoimmune and potentially alloimmune responses. We investigated the role of BTLA in a fully major histocompatibility complex-mismatched mouse islet transplant model. We report that anti-BTLA mAb (6F7) alone does not accelerate graft rejection. Rather, while CTLA4Ig alone improved allograft survival, the addition of anti-BTLA mAb to CTLA4Ig led to indefinite (>100 days) allograft survival. Immediately after treatment with anti-BTLA mAb and CTLA4Ig, islet allografts showed intact islets and insulin production despite a host cellular response, with local accumulation of Foxp3+ cells. We clearly demonstrate that combined therapy with anti-BTLA mAb and CTLA4Ig mice induced donor-specific tolerance, since mice accepted a second donor-specific islet graft without further treatment and rejected third party grafts. CTLA4Ig and anti-BTLA mAb limited the initial in vivo proliferation of CFSE-labeled allogeneic lymphocytes, and anti-BTLA mAb enhanced the proportion of PD-1 expressing T cells while depleting pathogenic BTLA+ lymphocytes. We conclude that targeting the BTLA pathway in conjunction with CTLA4Ig costimulatory blockade may be a useful strategy for promoting immunological tolerance in murine islet allografts.     

In vitro study of immune tolerance induced by CTLA4-Ig in bone transplantation: The effect on cell proliferation stimulated by lymphocytes and bone supernatant

To clarify the effect of CTLA4-lg on immune rejection of bone grafts, we observed the effect of CTLA4-lg on lymphocyte proliferation of BALB/C mice stimulated by lymphocytes and bone supernatant of C57BL/6 mice. The splenic lymphocytes and bone supernatant of C57BL/6 mice, as the stimulator cells and stimulator antigens, were cultured in vitro with the splenic lymphocyte of BALB/C mice. At the same time, CTLA4-lg at a dose of 5,10 or 20 &mgr;g/ml and L6 (as control) at 20 &mgr;g/ml were added. Six days later, the incorporation of 3 H-TdR was determined. Results indicated that CTLA4-Ig at a dose of 5, 10 or 20 &mgr;g/ml significantly inhibited the cell proliferation stimulated by lymphocytes and bone supernatant of C57BL/6 mice. The effect was non-cytotoxic. L6 showed no significant inhibition of cell proliferation. CTLA4-Ig can efficiently block the proliferation of alloresponsive T cell stimulated by lymphocytes and bone supernatant of C57BL/6 mice. This study provides a basis for further study of CTLA4-induced immune tolerance of bone grafts.     

Critical role of proinflammatory cytokine IL-6 in allograft rejection and tolerance

The proinflammatory cytokine IL-6 plays an important role in controlling T-cell differentiation, especially the development of Th17 and regulatory T cells. To determine the function of IL-6 in regulating allograft rejection and tolerance, BALB/c cardiac grafts were transplanted into wild-type or IL-6-deficient C57BL/6 mice. We observed that production of IL-6 and IFN-γ was upregulated during allograft rejection in untreated wild-type mice. In IL-6-deficient mice, IFN-γ production was greater than that observed in wild-type controls, suggesting that IL-6 production affects Th1/Th2 balance during allograft rejection. CD28-B7 blockade by CTLA4-Ig inhibited IFN-γ production in C57BL/6 recipients, but had no effect on the production of IL-6. Although wild-type C57BL/6 recipients treated with CTLA4-Ig rejected fully MHC-mismatched BALB/c heart transplants, treatment of IL-6-deficient mice with CTLA4-Ig resulted in graft acceptance. Allograft acceptance appeared to result from the combined effect of costimulatory molecule blockade and IL-6-deficiency, which limited the differentiation of effector cells and promoted the migration of regulatory T cells into the grafts. These data suggest that the blockade of IL-6, or its signaling pathway, when combined with strategies that inhibit Th1 responses, has a synergistic effect on the promotion of allograft acceptance. Thus, targeting the effects of IL-6 production may represent an important part of costimulation blockade-based strategies to promote allograft acceptance and tolerance.     

Blockade of LIGHT/HVEM and B7/CD28 signaling facilitates long-term islet graft survival with development of allospecific tolerance

BACKGROUND: Previous studies have shown that blockade of LIGHT, a T-cell costimulatory molecule belonging to the tumor necrosis factor (TNF) superfamily, by soluble lymphotoxin beta receptor-Ig (LTbetaR-Ig) inhibited the development of graft-versus-host disease. The cardiac allografts were significantly prolonged in LIGHT deficient mice. No data are yet available regarding the role of the LIGHT/HVEM pathway in more stringent fully allogeneic models such as skin and islet transplantation models. METHODS: Streptozotocin-induced chemical diabetic BALB/C mice underwent transplantation with allogeneic C57BL/6 islets and were treated with LTbetaR-Ig, CTLA4-Ig or a combination of both in the early peritransplant period. RESULTS: Administration of CTLA4-Ig or LTbeta R-Ig alone only increased graft survival to 55 days and 27 days respectively, whereas simultaneous blockade of both pathways significantly prolonged the islet allograft survival for more than 100 days. Long-term survivors were retransplanted with donor-specific (C57BL/6) islets and the grafted islets remained functional for more than 100 days. All of islet allografts were protected against rejection when the mixtures of 1x10(6) CD4+ T cells from tolerant mice and islet allografts were cotransplanted under the renal capsule of the na?ve BALB/c recipients. CONCLUSIONS: These data indicate that: 1) a synergistic effect for prolonged graft survival can be obtained by simultaneously blocking LIGHT and CD28 signaling in the stringent model of islet allotransplantation; 2) development of donor-specific immunological tolerance is associated with the presence of regulatory T-cell activity; and 3) local cotransplantation of the allografts with the regulatory T cells can effectively prevent allograft rejection and induce donor-specific tolerance in lymphocytes-sufficient recipients.     

小鼠异体皮移植创面使用细胞毒性T淋巴细胞抗原4-Ig重组腺病毒载体对其免疫功能的影响

目的　在小鼠背部移植异体皮后局部使用细胞毒性T淋巴细胞抗原 4 Ig(CTLA4 Ig)重组腺病毒载体 ,观察其对机体免疫功能的影响。　方法　将 6 0只BALB/c小鼠随机分为手术对照(A)组、CTLA4 Ig转染 (B)组及正常对照 (C)组 ,每组 2 0只。A、B组小鼠制作 1 .5cm× 1.5cm创面 ,移植同创面大小的C57BL小鼠皮肤后 ,A组小鼠创面涂抹不含腺病毒的交联聚丙烯酸树脂 (卡波姆霜 )0 .1g;B组小鼠创面涂抹含腺病毒的卡波姆霜 0 .1g,病毒滴度 5× 1 0 9/L。C组小鼠不作任何处理。术后 1d分别向 3组小鼠腹腔内注射体积分数 1 0 %绵羊红细胞 (SRBC)1ml。术后 7、1 4、2 1、2 8d收集血清进行凝集试验 ,检测SRBC抗体的效价 ,同时取BALB/c、C57BL及昆明小鼠的脾淋巴细胞作混合淋巴细胞培养 (MLC),观察CTLA4 Ig对脾淋巴细胞的抗原识别特异性及再次应答的影响。结果3组小鼠抗SRBC抗体效价组间比较 ,差异无显著性意义 (P >0.0 5 )。术后 1 4d内与A组比较 ,B组小鼠脾淋巴细胞与对C57BL小鼠脾淋巴细胞表现出特异性低反应 (P <0.0 5);1 4d后 ,A、B组的再次应答达到或超过C组 (P >0.0 5 )。结论　局部使用CTLA4 Ig重组腺病毒不影响小鼠的体液免疫功能 ,但可能引起系统性的特异性细胞免疫耐受。     

CTLA4 engagement is required for induction of murine liver transplant spontaneous tolerance.

Liver transplantation in mice is accepted spontaneously in all strain combinations. The mechanisms remain largely undefined. We hypothesize that signaling via the B7-CTLA4 receptor pathway is required for induction of liver transplant tolerance. Liver transplantation was performed from B10 (H2(b)) to C3H (H2(k)) mice. The recipients received anti-mouse CTLA4 mAb 0.25 mg i.p. every other day post-operatively. Liver grafts in anti-CTLA4 mAb treated recipients were acutely rejected. The allo-specific proliferative responses, anti-donor CTL and NK cell activities of GIC and SC and the serum levels of IFN-gamma and IL-2 from anti-CTLA4 mAb treated recipients were elevated significantly in comparison to the control mice. The frequency of IFN-gamma and IL-2 producing cells were markedly increased also in the anti-CTLA4 treated recipients. The immunohistology of liver grafts from anti-CTLA4 mAb treated mice showed extensively increased lymphocyte infiltration in the portal and general parenchymal areas, and expanded T-cell area in the spleen, with a reduction in the frequency of apoptotic cells observed by TUNEL staining compared with control mice. Thus CTLA4 signaling is critical for murine liver transplant tolerance induction. CTLA4 blockade promotes donor specific T-cell activation, cytotoxicity and Th1 polarization; protects alloreactive T cells from apoptotic death and induces liver allograft acute rejection.     

Blockade of the passive cell death pathway does not prevent tolerance induction to islet grafts

BACKGROUND: T-cell apoptosis is an important regulatory mechanism in transplant tolerance. The aim of this study was to identify specific apoptotic molecules important for tolerance induction. METHODS: Mice expressing the human Bcl-2 molecule in T cells or Bim -/- mice were used as islet allograft or rat islet xenograft recipients and treated with CTLA4-Fc and MR1 costimulation blockade. RESULTS: hBcl-2 transgenic mice and Bim -/- accepted islet allografts and rat islet xenografts for more than 100 days, similar to wildtype controls. Changes in the dose of the CTLA4-Fc and MR1 did not lead to differences in graft survival and there were no differences in the percentage of CD4+ T cells expressing Fas, CD25, or undergoing apoptosis. CONCLUSIONS: Inhibition of the passive cell death pathway in T cells did not block tolerance induction, suggesting that the mechanism by which apoptosis regulates the alloimmune response is more complex than first thought.     

Aggressive skin allograft rejection in CD28-/- mice independent of the CD40/CD40L costimulatory pathway.

CD28-/- mice have been utilized to study the role of B7/CD28 and B7-CTLA4 interactions. There is evidence that CTLA4 ligation may be critical for tolerance induction. The aim of the current study is to further investigate rejection responses of CD28-/- mice and to define the role of B7-CTLA4 interactions in the absence of the CD40 and CD28 pathways. Balb/c skin allografts were transplanted onto C57BL/6 (B6) wild type or CD28-/- mice treated with anti-CD40L, CTLA4-Ig, or combination blockade. To investigate the cellular mechanism of rejection in CD28-/- recipients, mice were treated with anti-CD4 or anti-CD8 antibodies prior to treatment with costimulation blockade. The fluoroscein dye CFSE was utilized to study T cell expansion in vivo. Surprisingly, treatment of B6 CD28-/- mice with CTLA4-Ig alone (MST 12d), anti-CD40L alone (MST 13d), or combined blockade (MST 13d) had no effect on allograft survival compared to untreated B6 CD28 mice (MST 11d). CD28-/- recipients depleted of CD4+ cells and treated with CTLA4-Ig, anti-CD40L, or combination blockade also did not have prolonged survival compared with untreated mice (MST 10d). In contrast, CD28-/- recipients depleted of CD8+ cells had markedly prolonged allograft survival when treated with either anti-CD40L alone (MST 49d) or with combination blockade (MST 57d). Studies utilizing CFSE demonstrated that CD28-/- CD8+ T cells are not defective in in vivo proliferation responses compared with wild type CD8 cells. Thus, CD28-/- CD8+ T cells are responsible for aggressive rejection responses of CD28-/- mice independent of the CD40 pathway. In addition, CD40L blockade does not result in CD4+ T cell tolerance in CD28 recipients, despite an intact B7-CTLA4 pathway.     

Peripheral blood dendritic cells in human end-stage heart failure and the early post-transplant period: evidence for systemic Th1 immune responses.

OBJECTIVES: Dendritic cells (DCs) are antigen presenting cells that play a central role in inflammation, allograft rejection and immune tolerance. Myeloid (mDC) and plasmacytoid (pDC) subsets regulate immune reactions by polarising naive T-helper cells into a Th1 or Th2 response, respectively. In this study we examined total peripheral blood DCs, mDC and pDC subsets in chronic heart failure (CHF) and clinical heart transplantation (HTx). METHODS: We compared 16 heart transplant patients before and after HTx to 14 healthy controls. Whole blood was collected pre-HTx and 1-week post-HTx from patients and at corresponding time-points from controls. All patients received induction and maintenance immunosuppression post-HTx. mDCs and pDCs were measured by flow cytometry and were further characterised for maturation and homing potential to the secondary lymphoid organs with CD83 and CCR7, respectively. Data were expressed as absolute numbers/microl whole blood, percentage (%) mDC or pDC of total blood DCs and % positive DCs for CD83 and CCR7. RESULTS: CHF patients had more peripheral blood DCs compared to controls (P<0.01) while only the mDC fraction was increased compared to controls (P=0.01). Percentage CD83(+) and CCR7(+) mDCs was also higher than control levels (P<0.05). One week post-HTx, total DCs, mDCs and pDCs decreased below controls (P<0.001). At the same time % mDCs in peripheral blood increased markedly compared to CHF and control levels (P<0.001). The %CD83(+) mDC, %CD83(+) pDC and %CCR7(+) mDC also returned to control levels and only %CCR7(+) pDC decreased below control levels (P=0.005). CONCLUSIONS: Total peripheral blood DCs are elevated during CHF due to an increase in the mature fraction of the mDC subset suggesting a possible Th1 response in end-stage heart failure. The decrease in total DCs and mature mDCs and pDCs seen post-HTx, probably reflects immunological quiescence through adequate immunosuppression. Peripheral blood DC monitoring may provide a new insight into mechanisms of heart failure and allograft rejection by safe weaning from immunosuppression after clinical HTx.     

CTLA4-Ig对肝细胞移植大鼠免疫耐受的作用及其机制

目的 探讨细胞毒性淋巴细胞相关抗原4融合蛋白(CTLA4-Ig)诱导肝细胞移植大鼠免疫耐受的作用及机制.方法 10%D-氨基半乳糖(D-gal)一次性腹腔注射建立大鼠急性药物性肝衰竭模型;采用肝脏原位灌注法分离纯化肝细胞,经脾脏移植后随机分为两组.实验组腹腔一次性注射CTLA4-Ig,对照组不予处理.两组均分别于术后第1、3、5、7天采外周血观察白细胞介素(IL)-2、肿瘤坏死因子(TNF)及肝功能变化;术后1周测两组大鼠外周血T细胞亚群,处死大鼠后取脾脏苏木素-伊红(HE)染色.结果 实验组谷丙转氨酶(ALT)、血清总胆红素(TBil)于术后第7天分别为(6.5±7.3)IU/ml、(5.1±1.6)mmol/L,低于对照组.术后治疗组IL-2含量明显下降,第7天达到(1. 3138±0.8508)ng/L,两组差异有统计学意义(P＜0.05);术后TNF含量两组之间差异无统计学差异(P＞0.05).外周血CD4+T细胞、CD4+/CD8+T细胞实验组分别为(37.3±7.2)%、(1.5±0.1)%,低于对照组(P＜0.05),CD8+T细胞两组差异无统计学意义(P＞0.05).术后第7天治疗组脾内仍可见肝细胞或肝细胞团,对照组见大量淋巴细胞浸润,但很少见肝细胞.结论 CTLA4-Ig能诱导经脾同种异体肝细胞移植大鼠免疫耐受,使急性肝衰大鼠肝功能得到改善.可能是抑制T淋巴细胞亚群,且主要是抑制CD4+T细胞,使CD4+/CD8+T细胞比值下降;抑制IL-2的分泌.

Abstract：

Objective To investigate the immunosuppressive effect of cytotoxic T Iymphocyte associated antigen 4 Ig fusion protein (CTLA4-Ig) in rat allograft hepatocyte transplantation model and the mechanisms. Methods Acute liver failure (ALF) model was established by intraperitoneal injection of 10% D-gal solution to SD rates. Collagenase perfusion was performed on SD rats to separate liver cells. SD rats with ALF were subjected to intrasplenic hepatocyte transplantation and randomly divided into two groups. The experimental group received intraperitoneal injection of CTLA4-Ig. The concentrations of interleukin (IL)-2 and tumor necrosis factor (TNF), liver function and histologicy were observed at the 1st,3rd, 5th, 7th day after operation and the T lymphocyte subsets were detected by using immunohistochemistry at the 7th day after operation. Results The levels of ALT and TBil were respectively (6. 5 ±7.3) IU/ml and (5.1 ± 1.6) mmol/L at the 7th day after operation and significantly decreased after injection of CTLA4-Ig ( P ＜ 0. 01 ). IL-2 concentration in the experimental group was ( 1.3138 ± 0. 8508 ) ng/L at the 7th day after operation and significantly decreased (P ＜0. 05). TNF had no significant difference between two groups after operation ( P ＞ 0. 05 ). T lymphocyte subsets, mainly CD4 + , in the experimental group was significantly decreased as compared with control group ( P ＜ 0. 05 ), so did the CD4 +/CD8 +. Histological changes: At the 7th day after operation, there were some hepatocytes in the spleen of the experimental group. But in the control group, the changes in the spleen were characterized by severe lymphocyte infiltration. There were no hepatocytes both groups. Conclusion CTLA4-Ig can induce rat allogeneic hepatocytes intrasplenic transplantation immune tolerance. It may improve the liver function of rats with ALF.CTLA4-Ig can decrease T lymphocyte subsets, mainly CD4 + and concentrations of IL-2.     

Achieving permanent survival of islet xenografts by independent manipulation of direct and indirect T-cell responses

Recent success in pancreatic islet allotransplantation has raised expectations but has equally highlighted the acute shortage of donor tissue. The use of xenogeneic tissue would help to address this shortage; however, strong cellular immunity limits the application of this approach. T-cell responses to xenogeneic tissues involve recognition of intact species-mismatched major histocompatibility complex (MHC) molecules, the direct pathway, and xenogeneic proteins presented as peptides by responder-type MHC molecules, the indirect pathway. In this study, we exploited the species difference to selectively and sequentially inhibit direct and indirect xenoresponses after transplantation of porcine islets into mice. Selective inhibition of the direct response was achieved using porcine CTLA4-Ig, which binds preferentially to pig versus mouse B7 molecules. Selective inhibition of the indirect response was achieved using murine CTLA4-Ig, which binds preferentially to mouse B7 molecules. Administration of porcine CTLA4-Ig alone caused modest prolongation of islet survival. Injection of murine CTLA4-Ig alone had a minimal effect. However, the injection of the porcine fusion protein early and the murine homolog late after grafting led to permanent survival of the porcine islets, in the absence of any other immunosuppression. These results suggest that a similar approach could have clinical utility in porcine islet xenotransplantation.     

A dendritic cell line genetically modified to express CTLA4-IG as a means to prolong islet allograft survival

BACKGROUND: Dendritic cells are potent antigen-presenting cells that bind allogeneic T cells. They are thus candidates for targeting immunoregulatory molecules to the alloreactive T cell compartment and suppressing the alloimmune response. METHOD: A dendritic cell line derived from the BALB/c mouse (H2d) was genetically modified to express the immunoregulatory molecule CTLA4-Ig. The ability of these dendritic cell transfectants to downregulate the alloimmune response was tested in an islet transplant model. Allogeneic C57Bl/6 (H2b) mice were rendered diabetic with streptozocin, and they received BALB/c islet (H2d) transplants. Mice were administered 25 million untransfected or CTLA4-Ig-transfected D2SC/1 cells i.v. on the day of islet transplantation and 6 days later[fnc]. RESULT: Mice treated with CTLA4-Ig-transfected D2SC/1 cells demonstrated prolonged allograft survival (mean = 20 days, median = 17 days, SD = 9.39) compared with mice treated with untransfected D2SC/1 cells (mean = 12 days, median = 11 days, SD=2.74) or untreated control mice (mean = 11 days, median = 11 days SD = 1.41). Third party allograft survival was not prolonged in mice receiving similar treatment. CONCLUSIONS: These results demonstrate that a genetically modified dendritic cell line can suppress the alloimmune response and prolong islet allograft survival in an allospecific manner. The findings also suggest that genetically modified dendritic cells may be useful in targeting alloreactive T cells and prolonging allograft survival.     

Nitric oxide and indoleamine 2,3-dioxygenase mediate CTLA4Ig-induced survival in heart allografts in rats

Cytotoxic T lymphocyte-associated antigen 4 immunoglobulin (CTLA4Ig) leads to transplantation tolerance in mice depending on indoleamine 2,3-dioxygenase (IDO). We have shown that CTLA4Ig induces indefinite heart allograft survival in rats and that nitric oxide (NO) was implicated in the in vitro active tolerogenic mechanisms mediated by dendritic cells (DCs). Here we studied the in vivo tolerogenic mechanisms by which CTLA4Ig induces graft survival in rats receiving a cardiac allograft. Treatment of recipients with the IDO inhibitor 1-methyltryptophan (1-MT) did not abrogate the indefinite graft survival observed with CTLA4Ig alone. This was also the case after administration of the inducible nitric oxide synthase inhibitor aminoguanidine when again, indefinite allograft survival was maintained. However, administration of both inhibitors led to acute rejection. We show that IDO and NO are responsible for the impaired capacity of DCs from CTLA4Ig-treated rats to stimulate allogeneic T cells. In conclusion, we show that NO and IDO mediate CTLA4Ig-induced tolerance in rat allograft recipients.     

Multiple Combination Therapies Involving Blockade of ICOS/B7RP-1 Costimulation Facilitate Long-Term Islet Allograft Survival

In recent years a series of novel costimulatory molecules have been identified, including inducible costimulator (ICOS). In a fully major histocompatibility complex (MHC)-mismatched mouse model of islet transplantation, we demonstrate that while monotherapy with CTLA4-Ig, CD40 ligand monoclonal antibody (CD40L mAb) or rapamycin each improves islet allograft survival, graft rejection eventually develops. Immunohistologic analysis of rejected grafts revealed increased ICOS expression, suggesting a role for this costimulatory molecule as an alternate pathway for T-cell activation. The combination of a blocking anti-ICOS mAb with each of the above therapies resulted in significantly improved islet allograft survival, confirming the importance of ICOS signaling in islet allograft rejection. Mechanistic studies conducted in mice treated with anti-ICOS mAb and rapamycin demonstrated a lack of donor-specific immunological tolerance and an absence of regulatory T-cell activity. However, a dramatic effect was seen on acute anti-donor responses whereby anti-ICOS mAb and rapamycin significantly reduced the initial expansion and function of alloreactive T cells. These data demonstrate that blockade of the ICOS/B7RP-1 pathway has potential therapeutic benefit given its role in enhancing islet allograft survival and regulating acute alloresponses in vivo.     

CTLA4-Ig基因对大鼠肝移植后免疫细胞浸润及细胞凋亡的影响

目的研究腺病毒介导的细胞毒性T淋巴细胞相关抗原4-Ig(cytolyticT-lymphocyteassociatedantigen4-Ig,CTLA4-Ig)基因对大鼠肝移植后移植物中免疫细胞浸润和细胞凋亡的影响。方法将大鼠原位肝移植模型分为排斥对照组、环孢素A(CsA)组和CTLA4-Ig组。分别于术后1,3,5,7,12d,用免疫组织化学法和缺口末端标记技术(TUNEL法)分别测定移植物中CTLA4-Ig基因的表达和巨噬细胞、CD8 T细胞浸润及细胞凋亡,并以病理形态学变化作参照。结果静脉注射重组CTLA4-Ig基因腺病毒7d后,大鼠肝脏CTLA4-Ig稳定表达,在肝移植60d后仍呈阳性;CTLA4-Ig组汇管区巨噬细胞、CD8 T细胞浸润明显较排斥对照组少;细胞凋亡指数在术后3、5和7d明显低于排斥对照组(P<0·01),汇管区巨噬细胞、CD8 T细胞浸润数和凋亡指数与排斥反应分级均显著相关。结论重组CTLA4-Ig基因腺病毒经静脉一次给药后能在大鼠肝脏稳定表达,并通过抑制移植物中免疫细胞浸润及移植物细胞凋亡,抑制移植后急性排斥反应。     

A limited course of soluble CD83 delays acute cellular rejection of MHC-mismatched mouse skin allografts

CD83 is a surface marker expressed on matured dendritic cells (DCs). It plays a pivotal role in the mediation of DC/T cell interaction and induction of T-cell activation. Previous studies have suggested that a soluble form of CD83 could suppress DC maturation and inhibit T-cell activation and, as a result, it can prevent paralysis associated with experimental autoimmune encephalomyelitis. Here, we explored its potential effect on allograft rejection in a fully major histocompatibility complex-mismatched murine skin transplantation model. A form of mouse soluble CD83 (CD83-Ig) fused the extracellular domain of murine CD83 with human IgG1alpha Fc tail was purified from transfected COS-7 cell. It was found that the treatment of recipient mice with CD83-Ig significantly delayed allograft rejection. Especially, when T cells originated from recipients treated with CD83-Ig re-stimulated with donor-specific splenocytes, they showed a significant reduced responding capability as compared with that of originated from control recipients. In line with these results, a reduction for serum IFN-gamma and IL-2 and a decreased mRNA expression of IFN-gamma and IL-2 in allograft infiltrated immune cells were also observed. Our results suggest that CD83-Ig could be useful for the treatment of allograft rejection in combination with other therapeutic strategies.     

Changes in expression of T-cell activation-related molecules and cytokines during tolerance induction in an allogeneic skin transplantation murine model

Bone marrow transplantation after treatment with busulfan and costimulatory blockade with monoclonal antibodies (mAb) cytotoxic T lymphocyte antigen 4 (CTLA4)-Ig and anti-CD154 mAb or two-signal blockade using anti-CD45RB and anti-CD154 mAb are nonmyeloablative treatment regimens for allogeneic transplantation. There may be differences in the mechanisms of donor cell engraftment and reactive cell deletion by which these regimens induce donor-specific tolerance. Therefore, this study was performed to investigate changes in T cells and cytokines during tolerance induction toward allogeneic skin grafts. BALB/c and C57BL/6 mice were used as donors and recipients, respectively. Skin and bone marrow transplantations were performed and busulfan was administered. Three groups were treated with mAb as follows: group 1, anti-CD154 mAb; group 2, anti-CD154 plus anti-CD45RB mAb; and group 3, anti-CD154 mAb plus CTLA4-Ig. The proportions of CD4+ or CD8+ T cells and the expression of CD45RB isoforms on splenocytes were measured using flow cytometry and the production of cytokines by CD4+ T cells using enzyme-linked immunosorbent assay. Group 2 showed a significant reduction in the proportions of CD8+ T cells and CD45RB high isoforms compared with groups 1 and 3. The levels of interleukin (IL)-2 and IL-4 in group 2 were lower and higher than those of groups 1 and 3, respectively. In conclusion, the combined use of anti-CD154 and anti-CD45RB mAb decreases the CD8+ T-cell population and the expression of CD45RB, resulting in a Th2 cytokine profile, which may be a characteristic mechanism leading to donor cell engraftment and reactive cell deletion for donor-specific tolerance.     

Proliferative and cytokine responses in CTLA4-Ig-treated diabetic NOD mice transplanted with microencapsulated neonatal porcine ICCs

Our goal is to develop effective islet xenografts for treating human diabetes. We have studied microencapsulated neonatal porcine islet cell clusters (ICCs) transplanted intraperitoneally in spontaneously diabetic NOD mice, where they function to maintain normoglycemia in the autoimmune host. Nonencapsulated neonatal porcine ICCs functioned for 4.5 +/- 0.5 days before being rejected; encapsulation prolonged graft function to 17 +/- 2 days. CTLA4-Ig treatment did not enhance the survival of nonencapsulated ICCs. However, CTLA4-Ig treatment significantly extended the function of encapsulated ICCs to 73 +/- 5 days. Histological analyses demonstrated a profuse pericapsular cellular reaction associated with rejection of encapsulated islet xenografts in untreated mice, while this reaction was significantly reduced in CTLA4-Ig-treated mice. To study mechanisms of xenograft rejection in this model, we analyzed proliferative responses to neonatal porcine ICCs and cytokines present in the peritoneal cavities of transplanted mice. Spleen cells from both CTLA4-Ig-treated and untreated rejecting NODs exhibited vigorous proliferation in the absence of antigenic stimulation, suggesting prior activation in vivo, while splenocytes from CTLA4-Ig-treated NODs with functioning grafts had low proliferative levels, equal to controls. Islet-specific proliferation was not detected in islet-rejecting mice, perhaps due to their high background levels. With the exception of elevated IL-6 levels, empty capsules did not provoke a significant peritoneal cytokine response compared with sham surgery or untransplanted control mice. However, IL-5, IL-12, TGF-beta, and IL-1beta were significantly elevated in NODs receiving encapsulated neonatal porcine ICCs compared with untransplanted controls. There were no significant differences between peritoneal cytokine concentrations in CTLA4-Ig-treated mice with long-term functioning grafts compared to mice that rejected grafts at earlier time points. We conclude that the combination of donor islet microencapsulation and brief treatment of the recipient with co-stimulatory blockade delays sensitization of the host, possibly by altering mechanism(s) for recruitment and/or activation of host effector cells.     

CTLA4ig induces long-term graft survival of allogeneic skin grafts and totally inhibits T-cell proliferation in LFA-1-deficient mice

BACKGROUND: It was recently shown that some strains of mice are capable of rejecting transplants independently of B7 and CD40L signaling and that this rejection is mediated by CD8(+) T cells. LFA-1 is known to be important for CD8(+) T cell activation and cytotoxicity. Therefore, blockade of LFA-1 could be important in overcoming costimulation blockade, CD8(+) T-cell-mediated, resistant rejection. The purpose of this study was to define the effect of combined blockade of the LFA-1 and B7 costimulation pathways on the alloimmune response in mice. METHODS: Allogeneic skin transplantation was performed using BALB/c mice as donors and C57BL/6J wild-type or LFA-1-deficient (CD11a(-/-)) mice as recipients. CTLA4Ig or anti-LFA-1 was administered either as an induction or a prolonged therapy. Mixed lymphocyte reactions were conducted to study the effect of CTLA4Ig on T-cell proliferation in CD11a(-/-) mice. RESULTS AND CONCLUSIONS: Administration of CTLA4Ig completely inhibits CD11a(-/-) T-cell proliferation in response to alloantigens and significantly improved skin allograft survival in CD11a(-/-) mice. Prolonged treatment of wild-type recipient mice with CTLA4Ig and anti-LFA-1 increased median survival time to 45.5 days compared with 16 days after induction therapy, but it was not sufficient to induce indefinite allograft survival in this model.