Fas ligand, tumor necrosis factor-alpha expression, and apoptosis during allograft rejection and tolerance

Identification of cell-free DNA methylation patterns unique to the human left ventricle as a potential indicator of acute cellular rejection

Increased levels of donor-derived cell-free DNA (dd-cfDNA) in recipient plasma have been associated with rejection after transplantation. DNA sequence differences have been used to distinguish between donor and recipient, but epigenetic differences could also potentially identify dd-cfDNA. This pilot study aimed to identify ventricle-specific differentially methylated regions of DNA (DMRs) that could be detected in cfDNA. We identified 24 ventricle-specific DMRs and chose two for further study, one on chromosome 9 and one on chromosome 12. The specificity of both DMRs for the left ventricle was confirmed using genomic DNA from multiple human tissues. Serial matched samples of myocardium (n = 33) and plasma (n = 24) were collected from stable adult heart transplant recipients undergoing routine endomyocardial biopsy for rejection surveillance. Plasma DMR levels increased with biopsy-proven rejection grade for individual patients. Mean cellular apoptosis in biopsy samples increased significantly with rejection severity (2.4%, 4.4% and 10.0% for ACR 0R, 1R, and 2R, respectively) but did not show a consistent relationship with DMR levels. We identified multiple DNA methylation patterns unique to the human ventricle and conclude that epigenetic differences in cfDNA populations represent a promising alternative strategy for the non-invasive detection of rejection.

Avenues to molecular imaging of dying cells: Focus on cancer

Successful treatment of cancer patients requires balancing of the dose, timing, and type of therapeutic regimen. Detection of increased cell death may serve as a predictor of the eventual therapeutic success. Imaging of cell death may thus lead to early identification of treatment responders and nonresponders, and to “patient‐tailored therapy.” Cell death in organs and tissues of the human body can be visualized, using positron emission tomography or single‐photon emission computed tomography, although unsolved problems remain concerning target selection, tracer pharmacokinetics, target‐to‐nontarget ratio, and spatial and temporal resolution of the scans. Phosphatidylserine exposure by dying cells has been the most extensively studied imaging target. However, visualization of this process with radiolabeled Annexin A5 has not become routine in the clinical setting. Classification of death modes is no longer based only on cell morphology but also on biochemistry, and apoptosis is no longer found to be the preponderant mechanism of cell death after antitumor therapy, as was earlier believed. These conceptual changes have affected radiochemical efforts. Novel probes targeting changes in membrane permeability, cytoplasmic pH, mitochondrial membrane potential, or caspase activation have recently been explored. In this review, we discuss molecular changes in tumors which can be targeted to visualize cell death and we propose promising biomarkers for future exploration.

Heme oxygenase-1-transduced bone marrow mesenchymal stem cells in reducing acute rejection and improving small bowel transplantation outcomes in rats

Background

We determined whether bone marrow mesenchymal stem cells (BMMSCs) transduced with heme oxygenase-1 (HO-1), a cytoprotective and immune-protective factor, could improve outcomes for small bowel transplantation (SBTx) in rats.

Methods

We performed heterotopic SBTx from Brown Norway rats to Lewis rats, before infusing Ad/HO-1-transduced BMMSCs (Ad/HO-1/BMMSCs) through the superficial dorsal veins of the penis. Respective infusions with Ad/BMMSCs, BMMSCs, and normal saline served as controls. The animals were sacrificed after 1, 5, 7, or 10 days. At each time point, we measured small bowel histology and apoptosis, HO-1 protein and mRNA expression, natural killer (NK) cell activity, cytokine concentrations in serum and intestinal graft, and levels of regulatory T (Treg) cells.

Results

The saline-treated control group showed aggravated acute cellular rejection over time, with mucosal destruction, increased apoptosis, NK cell activation, and upregulation of proinflammatory and immune-related mediators. Both the Ad/BMMSC-treated group and the BMMSC-treated group exhibited attenuated acute cellular rejection at an early stage, but the effects receded 7 days after transplantation. Strikingly, the Ad/HO-1/BMMSC-treated group demonstrated significantly attenuated acute cellular rejection, reduced apoptosis and NK cell activity, and suppressed concentrations of inflammation and immune-related cytokines, and upregulated expression of anti-inflammatory cytokine mediators and increased Treg cell levels.

Conclusion

Our data suggest that Ad/HO-1-transduced BMMSCs have a reinforced effect on reducing acute rejection and protecting the outcome of SBTx in rats.

Reduction of acute rejection by bone marrow mesenchymal stem cells during rat small bowel transplantation

Background

Bone marrow mesenchymal stem cells (BMMSCs) have shown immunosuppressive activity in transplantation. This study was designed to determine whether BMMSCs could improve outcomes of small bowel transplantation in rats.

Methods

Heterotopic small bowel transplantation was performed from Brown Norway to Lewis rats, followed by infusion of BMMSCs through the superficial dorsal veins of the penis. Controls included rats infused with normal saline (allogeneic control), isogeneically transplanted rats (BN-BN) and nontransplanted animals. The animals were sacrificed after 1, 5, 7 or 10 days. Small bowel histology and apoptosis, cytokine concentrations in serum and intestinal grafts, and numbers of T regulatory (Treg) cells were assessed at each time point.

Results

Acute cellular rejection occurred soon after transplantation and became aggravated over time in the allogeneic control rats, with increase in apoptosis, inflammatory response, and T helper (Th)1/Th2 and Th17/Treg-related cytokines. BMMSCs significantly attenuated acute cellular rejection, reduced apoptosis and suppressed the concentrations of interleukin (IL)-2, IL-6, IL-17, IL-23, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ while upregulating IL-10 and transforming growth factor (TGF)-β expression and increasing Treg levels.

Conclusion

BMMSCs improve the outcomes of allogeneic small bowel transplantation by attenuating the inflammatory response and acute cellular rejection. Treatment with BMMSCs may overcome acute cellular rejection in small bowel transplantation.

Expression and prognostic value of FAS receptor/FAS ligand and TrailR1/TrailR2 in acute myeloid leukemia

We studied the expressions of FR, FL, TR1, and TR2 on blasts and T cells from 71 patients with acute myeloid leukemia (AML) and correlated expression rates with the clinical course. Compared to AML-blasts we found higher co-expressions on healthy myeloid and T cells. Expression of all markers on blasts and on T cells was similar in different subtypes and acute stages of AML. Compared to the non-responders (n = 7) responders to the AML Cooperative Group-therapy (n = 22) presented with higher proportions of blasts co-expressing the four markers (FR: 32 vs 15%; FL: 15 vs 13%; TR1: 72 vs 37%; TR2: 24 vs 23%) or T cells (FR: 88 vs 71%; FL: 76 vs 56%; TR1: 96 vs 44%; TR2: 54 vs 42%). Patients with higher expression rates of TR1 on blasts (≥ 48%) and on T cells (≥ 67%) were characterized by a prolonged survival. In summary, our data show a variable expression of FR, FL, TR1 and TR2 on blasts or T cells in different subgroups of AML. Higher co-expression rates of FR, FL, TR1 and TR2 were characterized by a better prognosis for the patients with respect to achieve a remission and to survive. Functional analyses should be performed to find out those patients in who induced upregulation of these markers could contribute to overcome drug resistance.

Apoptosis and acute cellular rejection in human heart transplants

INTRODUCTION AND OBJECTIVES

Apoptosis has been implicated in the pathophysiology of various forms of heart disease. Acute cellular rejection leads to morbidity after heart transplantation and invasive techniques are needed for its diagnosis. We investigated the presence of cardiomyocyte apoptosis in transplanted hearts, its progression, its relationship with rejection, and the possibility that serological markers of apoptosis can be used to detect rejection noninvasively.

METHODS

Overall, 130 endomyocardial biopsies obtained sequentially from 14 consecutive patients during the first 6 months following heart transplantation underwent histochemical analysis. The degree of acute rejection was determined, myocyte apoptosis was assessed using the TUNEL method, and caspase-3 activity was measured. In the first 10 patients, soluble Fas, tumor necrosis factor-alpha (TNFα) and interleukin 6 levels were determined in serum collected at biopsy.

RESULTS

Apoptotic cells were detected in 81.5% of biopsies. No significant correlation was found between the apoptotic index and either the degree of rejection or the time from transplantation; there was only a trend to higher values during prolonged episodes of rejection, which did not reach statistical significance. An inverse correlation was observed between the degree of rejection and the TNFα level (rs=-0.33; P=.003). There was no correlation with any other variable.

CONCLUSIONS

Cardiomyocyte loss due to apoptosis was observed in transplanted hearts, but no correlation was observed with either acute rejection or the time from transplantation. Our findings suggest there could be an inverse correlation between rejection and the serum TNFα level. No serum parameter evaluated was regarded as suitable for the noninvasive diagnosis of acute rejection.

Perioperative infliximab application ameliorates acute rejection associated inflammation after intestinal transplantation

As we have shown in the past, acute rejection-related TNF-α upregulation in resident macrophages in the tunica muscularis after small bowel transplantation (SBTx) results in local amplification of inflammation, decisively contributing to graft dysmotility. Therefore, the aim of this study is to investigate the effectiveness of the chimeric-monoclonal-anti-TNF-α antibody infliximab as perioperative single shot treatment addressing inflammatory processes during acute rejection early after transplantation. Orthotopic, isogenic and allogenic SBTx was performed in rats (BN-Lewis/BN-BN) with infliximab treatment. Vehicle and IV-immunoglobulin-treated animals served as controls. Animals were sacrificed after 24 and 168 h. Leukocyte infiltration was investigated in muscularis whole mounts by immunohistochemistry, mediator mRNA expression by Real-Time-RT-PCR, apoptosis by TUNEL and smooth muscle contractility in a standard organ bath. Both, infliximab and Sandoglobulin® revealed antiinflammatory effects. Infliximab resulted in significantly less leukocyte infiltration compared to allogenic controls and IV-immunoglobulin, which was accompanied by lower gene expression of MCP-1 (24 h), IFN-γ (168 h) and infiltration of CD8-positive cells. Smooth muscle contractility improved significantly after 24 h compared to all controls in infliximab treated animals accompanied by lower iNOS expression. Perioperative treatment with infliximab is a possible pharmaceutical approach to overcome graft dysmotility early after SBTx.

Cyclic AMP prolongs graft survival by suppressing apoptosis and inflammatory gene expression in acute cardiac allograft rejection

This study was designed to investigate the effects of cAMP on immune regulation and apoptosis during acute rat cardiac allograft rejection. We found that the production of immune markers such as inflammatory cytokines (IL-1beta, IL-6, and TNF-alpha), iNOS expression, and nitric oxide (NO) production, was significantly increased in the blood and transplanted hearts of allograft recipients, but not of isograft controls. These increases were effectively suppressed by the administration of the membrane permeable cAMP analog dibutyryl cAMP (db-cAMP). Administration of db-cAMP reduced allograft-induced elevation of several biochemical markers, such as adhesion molecule expression, iron-nitrosyl complex formation, caspase-3 activation, and apoptotic DNA fragmentation in an animal model. Furthermore, treatment of allograft recipients with db-cAMP prolonged median graft survival to 11 days compared with a median graft survival time of 8 days in saline-treated allograft recipients. These results suggest that db-cAMP exerts a beneficial effect on murine cardiac allograft survival by modulating allogeneic immune response and cytotoxicity.

Perioperative glycine treatment attenuates ischemia/reperfusion injury and ameliorates smooth muscle dysfunction in intestinal transplantation

BACKGROUND

Ischemia/reperfusion evokes a functionally relevant inflammatory response within the muscularis propria of small bowel grafts by activation of resident macrophages and leukocyte recruitment. We hypothesized that immunomodulatory perioperative treatment with glycine attenuates the proinflammatory cascade and improves smooth muscle dysfunction of small bowel grafts.

METHODS

Orthotopic SBTx was performed in Lewis rats. Glycine (1 mg/g body weight) was infused (0.1 mL/g/hr) for 2 hr before harvest as preconditioning in the donor, and for 2 hr from the onset of reperfusion in the recipient. Transplanted vehicle (isotonic saline)-treated animals and naive animals served as controls. Rats were sacrificed after 3 hr and 24 hr. Leukocyte infiltration was investigated in muscularis whole mounts by immunohistochemistry. Mediator mRNA expression was determined by real-time-PCR. Jejunal circular smooth muscle contractility was assessed in a standard organ bath.

RESULTS

Compared with vehicle controls, glycine-treated graft muscularis expressed a significant alleviation in mRNA peak expression for IL-6, IL-1beta, ICAM-1, MCP-1, TNFalpha, COX-2, and iNOS. Also glycine-treated grafts exhibited significantly less infiltration with ED-1-positive macrophages and MPO-positive neutrophils as well as reduced apoptosis. Concurrent to these results, vehicle controls showed an 80% decrease in smooth muscle contractility, whereas glycine-treated animals exhibited only a 40% decrease in contractile activity compared with controls.

CONCLUSIONS

The data indicate that perioperative glycine treatment reduces the molecular and cellular inflammatory response within the grafts and improves smooth muscle dysfunction after transplantation. Therefore, the glycine-activated chloride channel on resident and infiltrating leukocytes could be a promising pharmacologic target to attenuate ischemia/reperfusion injury after ITx.

Reactive oxygen and reactive nitrogen as signaling molecules for caspase 3 activation in acute cardiac transplant rejection

Apoptosis is a significant factor in cardiac dysfunction and graft failure in cardiac rejection. In this study, we examined potential signaling molecules responsible for caspase 3 activation in a model of acute cardiac allograft rejection. The roles of reactive oxygen species (ROS) and nitric oxide (NO) were determined in untreated allografts and allograft recipients treated with either cyclosporine (CsA), alpha-phenyl-t-butylnitrone (PBN, a spin-trapping agent), vitamin C (VitC), Mn(III)tetrakis (1-methyl-4-pyridyl)porphyrin); MnTmPyP, a superoxide dismutase (SOD) mimetic), or L-(1-iminoethyl)lysine) (L-NIL), an inhibitor of inducible NO synthase (iNOS) enzyme activity. Graft tissue was taken for measuring superoxide radical production, Western blotting, and direct measurement of caspase 3 activity. Activation of caspase 3 in untreated allografts was revealed by the appearance of cleaved caspase 3 from pro-caspase 3 by Western blotting and functional caspase 3 catalytic activity. CsA or PBN inhibited iNOS expression and caspase 3 activity. VitC and MnTmPyP did not alter iNOS expression or decrease NO levels but did inhibit caspase 3 activity. In contrast, L-NIL completely inhibited the increase in NO production without altering iNOS expression and inhibited caspase 3 activity. The prevention of TUNEL staining by MnTmPyP and L-NIL confirmed downstream effects of superoxide and NO on apoptosis. These studies indicate that both superoxide and NO (precursors of peroxynitrite formation) play a significant role in caspase 3 activation in cardiac allograft rejection.

Endothelial cell activation contributes to the release of procoagulant microparticles during acute cardiac allograft rejection

BACKGROUND

Circulating procoagulant microparticles are reliable markers of vascular damage. The microparticle phenotypes provide additional information reflecting the nature of cell injury. This study assessed procoagulant microparticle levels and phenotypes in the diagnosis of acute allograft rejection after heart transplantation.

METHODS

Microparticles were prospectively investigated in the venous blood of 64 heart transplant patients, 23 with allograft rejection mainly of low score, and 41 without a rejection episode. Plasma concentrations of cytokines, cytoadhesins, and platelet activation markers were determined.

RESULTS

By univariate analysis, the mean time elapsed from heart transplant, cold ischemia time, E-selectin-, Fas- and tissue factor-bearing microparticles were associated with allograft rejection. By multivariate analysis, E-selectin-microparticle levels appeared independently associated with allograft rejection, even when other significant variables were included in the model (odds ratio, 9.8; 95% confidence interval, 1.36-71.4; p = 0.023).

CONCLUSION

The pattern of procoagulant microparticles released during acute allograft rejection suggests endothelial cell activation and Fas-mediated apoptosis. E-selectin-bearing microparticles appeared as an independent marker of acute allograft rejection that was still informative after adjustment for graft characteristics.

FasL expression in hepatic antigen-presenting cells and phagocytosis of apoptotic T cells by FasL+ Kupffer cells are indicators of rejection activity in human liver allografts

Fas-Fas ligand (FasL) interaction and apoptosis are important in the mechanism of allograft rejection. However, the interaction between donor and recipient cells, specifically focusing on antigen-presenting cells (APCs), under various conditions is poorly understood in human liver allografts. FasL expression on APCs, its association with apoptosis, and the origin of apoptotic lymphocytes in human liver allografts were assessed by immunohistochemistry and in situ hybridization. We found increased expression of FasL on Kupffer cells (KCs) and endothelium in acute cellular rejection (n = 20) and to lesser extent in chronic rejection (n = 6) and septic cholangitis (n = 5) compared with stable grafts and normal controls. In addition, the graft specificity of infiltrating T cells was confirmed by polymerase chain reaction examination of T-cell receptor-gamma loci. T-cell apoptosis occurred at a higher rate in acute cellular rejection than in chronic rejection or septic cholangitis. The number of apoptotic bodies derived from recipient lymphocytes correlated with the severity of rejection and was reversed by treatment. FasL(+) KCs phagocytosed CD4(+) interferon-gamma(+) T cells, rather than CD4(+) interleukin-4(+) T cells, suggesting a role of KCs in regulating CD4(+) T-cell subset differentiation. In conclusion, our data suggest that FasL expression on APCs and phagocytosis of apoptotic T cells by FasL(+) KCs are indicators of rejection activity in human liver allografts.

Combination Treatment with Donor-Specific Transfusions and Cyclosporine A Induces Long-Term Survival of Cardiac Allografts in Miniature Swine

BACKGROUND

To evaluate whether pretransplant donor-specific transfusions (DST) can induce tolerance to cardiac allografts in large animals, heterotopic cardiac transplants were performed across a class I MHC barrier in inbred miniature swine.

METHODS

Experimental animals received two DSTs, each containing 1.4x10 viable peripheral blood mononuclear cells, 14 and 7 days prior to transplantation together with a 12-day course of cyclosporine (CyA) (13 mg/kg IV) starting on postoperative day (POD) 0.

RESULTS

Untreated (n=2) and DST-only (n=2) treated control animals rejected between POD 6 and 8. Animals treated with CyA alone (n=3) exhibited graft survival to 53, 52 and 59 days. In contrast, the combination of DST and CyA (n=3) led to stable graft function for >200 days. Long-term survivors maintained peripheral CML response against donor antigen. Following DSTs, the donor-specific proliferative response of CD8+ recipient T cells was significantly increased (P=0.011), and a significant number of CD8+ T cells underwent apoptosis (10.1% on POD 0; 5.2% on POD -14; P=0.04). None of the DST-treated animals developed donor-specific antibodies.

CONCLUSIONS

These results are the first to demonstrate the ability of DST to induce operational tolerance to cardiac allografts in large animals, and they suggest that peripheral mechanisms of tolerance mediate this effect.

Correlation of CD95 and soluble CD95 expression with acute rejection status of liver transplantation

AIM: To analyze the expression levels of soluble form of CD95, CD95 ligand (sCD95 and sCD95L, respectively) in plasma and CD95 expression on CD3⁺ cells in liver-transplanted recipients with acute rejection (AR).

METHODS: Peripheral blood mononuclear cells (PBMCs) were isolated from 30 clinically liver transplanted recipients. CD95 expression on CD3⁺ cells was quantitatively measured by two-color fluorescence activated cell sorter (FACS) analysis. Lymphocyte surface phenotypes of CD4, CD8, CD16 and CD56 were determined by flow cytometry. Plasma levels of sCD95 and sCD95L were detected by Enzyme Linked-Immuno-Sorbent Assay (ELISA). The results were compared with that from normal healthy volunteers (n = 15 individuals).

RESULTS: FACS analysis showed that CD95 expression on CD3⁺ T cells was significantly increased in liver transplanted recipients with AR compared to that in stable recipients without rejection and infection or healthy individuals who did not undergo transplantation (18676.93±11588.34/molecule, 6848.20±1712.96/molecule, 6418.01±2001.95/molecule, respectively, P<0.01). Whereas no significant difference was seen between liver-transplanted stable recipients and healthy individuals. Furthermore, no significant differences were detected between each group with CD4/CD8 ratio or the percentage of CD16⁺56⁺ cells. Plasma levels of sCD95 were significantly higher in transplanted recipients with AR compared to that in stable recipients or healthy individuals (391.88±196.00, 201.37±30.30, 148.83±58.25 pg/mL, respectively, P<0.01). In contrast, the plasma levels of sCD95L in liver- transplanted recipients were not significantly different from that in healthy individuals.

CONCLUSION: The present results indicate that the increased CD95 expression on CD3⁺ cells and the increased levels of sCD95 in plasma may modify the immunological situation of the recipients after transplantation or represent the ongoing graft rejection.

Induction of tolerance using Fas ligand: a double-edged immunomodulator

Apoptosis mediated by Fas ligand (FasL) interaction with Fas receptor plays a pivotal regulatory role in immune homeostasis, immune privilege, and self-tolerance. FasL, therefore, has been extensively exploited as an immunomodulatory agent to induce tolerance to both autoimmune and foreign antigens with conflicting results. Difficulties associated with the use of FasL as a tolerogenic factor may arise from (1) its complex posttranslational regulation, (2) the opposing functions of different forms of FasL, (3) different modes of expression, systemic versus localized and transient versus continuous, (4) the level and duration of expression, (5) the sensitivity of target tissues to Fas/FasL-mediated apoptosis and the efficiency of antigen presentation in these tissues, and (6) the types and levels of cytokines, chemokines, and metalloproteinases in the extracellular milieu of the target tissues. Thus, the effective use of FasL as an immunomodulator to achieve durable antigen-specific immune tolerance requires careful consideration of all of these parameters and the design of treatment regimens that maximize tolerogenic efficacy, while minimizing the non-tolerogenic and toxic functions of this molecule. This review summarizes the current status of FasL as a tolerogenic agent, problems associated with its use as an immunomodulator, and new strategies to improve its therapeutic potential.

An introduction to death receptors in apoptosis

Apoptosis is a source of much research interest across many fields, including developmental biology, immunology and oncology. As the exact pathways of this process are identified, so too are potential avenues for therapeutic application. Death receptors are important in inducing apoptosis and together with their ligands have become a source of attention as potential therapeutic agents. This review provides an introduction to the role of death receptors in apoptosis, together with a look at possible areas where this information may be applied therapeutically.

Induction of long-term cardiac allograft survival by heme oxygenase-1 gene transfer

Elevated expression of heme oxygenase-1 (HO-1), an intracellular enzyme that degrades heme into carbon monoxide (CO), biliverdine and free iron, has anti-inflammatory and antiapoptotic effects in diverse models. Here, we analyzed the effects of specific overexpression of HO-1 following adenovirus-mediated (AdHO-1) gene transfer in an acute cardiac allograft rejection model. The intragraft (i.g.) injection of AdHO-1 into cardiac allografts, as well as intramuscular (i.m.) or intravenous (i.v.) administration, prolonged allograft survival with, respectively, 13.3, 62.5 and 80% of the grafts surviving long term (>100 days), whereas control grafts were rejected with acute kinetics. HO-1 overexpression was associated with inhibited allogeneic responses in MLRs using graft-infiltrating leukocytes and splenocytes, but not with lymph node cells. The inhibition of splenocyte proliferation was mediated by soluble factors and was dependent on the presence of APCs, since purified T cells proliferated normally. i.v. but not i.g. AdHO-1 administration decreased the number of graft-infiltrating leukocytes, cytokine mRNA accumulation and apoptosis in transplanted hearts, whereas i.v. and i.g. AdHO-1 did not modify normal immune responses against cognate antigens, indicating that there was no general immunosuppression. These results indicate that HO-1 overexpression prolongs the survival of vascularized allografts by promoting tolerogenic mechanisms acting on allogeneic cellular immune responses.

The role of TNF-related activation-induced cytokine-receptor activating NF-kappa B interaction in acute allograft rejection and CD40L-independent chronic allograft rejection

We analyzed the role of TNF-related activation-induced cytokine (TRANCE), a member of the TNF family expressed on activated T cells that shares functional properties with CD40L, and its receptor-activating NF-kappaB (RANK) which is mostly expressed on mature dendritic cells, during allogenic responses in vivo using a rodent heart allograft model. TRANCE mRNA was strongly up-regulated in acutely rejected allografts on days 4 and 5 posttransplantation whereas RANK was detected as early as day 1 but did not show further up-regulation during the first week. Immunofluoresence analyses of heart allografts showed that 80 and 100% of TRANCE and RANK-expressing cells were T cells and APCs, respectively. We show for the first time that short-term TRANCE blockade using a mouse RANKIg fusion molecule can significantly prolong heart allograft survival in both rat and mouse models. Similarly, rat heart allografts transduced with a RANKIg encoding recombinant adenovirus exhibited a significant prolongation of survival (14.3 vs 7.6 days, p < 0.0001). However, TRANCE blockade using RANKIg did not appear to inhibit allogeneic T and B cell priming humoral responses against RANKIg. Interestingly, TRANCE blockade induced strong up-regulation of CD40 ligand (CD40L) mRNA in allografts. Combined CD40L and TRANCE blockade resulted in significantly decreased chronic allograft rejection lesions as well as allogeneic humoral responses compared with CD40L blockade alone. We conclude that TRANCE-RANK interactions play an important role during acute allograft rejection and that CD40L-independent allogeneic immune responses can be, at least in part, dependent on the TRANCE pathway of costimulation.

Transplantation immunology 2003: simplified approach

Transplantation has been performed clinically for four decades and has become the standard of care for end-stage organ failure. Understanding of the immunobiology of transplantation has made tremendous advances, but knowledge still lags behind the clinical use. As a result, nonspecific immunosuppression remains the standard therapy. This article presents an overview of current knowledge of the immunobiology of solid organ transplantation, with emphasis on T-cell activation (antigen presentation, CoS) and cellular allograft (transplantation) immunity. The molecular events of T-cell activation, with some emphasis on the sites of action of modern immunosuppression, are reviewed. A simplified approach to understanding the immunobiology and strategy of maintenance immunosuppression is discussed. Key early and late steps in T-cell activation and the sites of action of immunosuppressive agents are reviewed. The required cellular interactions for the alloresponse and the targets of biologic agents used in transplants are reviewed. Special considerations for the immunology in neonates, infants, and children as recipients are provided. Understanding the immunobiology of transplantation is key to making decisions about children with transplants, developing better protocols, and creating tolerance in the future.

Overexpression of soluble fas attenuates transplant arteriosclerosis in rat aortic allografts

BACKGROUND

The killing of vascular cells by activated macrophages is an important step in the process of destabilization of the arterial wall. The death receptor Fas is implicated in vascular cell death. Hence, we extended our studies in a rat aortic allograft model, using adenovirus-mediated overexpression of soluble Fas (sFas) to block Fas binding to Fas ligand (Fas-L). The contribution of Fas to vascular cell injury and consequent transplant arteriosclerosis was investigated.

METHODS AND RESULTS

Activated monocytes in the presence of macrophage colony-stimulating factor induce endothelial cell apoptosis in vitro, which was significantly inhibited by adenovirus-mediated sFas overexpression. Next, donor rat abdominal aortas were either untreated or transduced with adenoviruses encoding (1) rat soluble Fas (Ad3rsFas), (2) no insert (Ad3Null), and (3) beta-galactosidase (Ad3nBg). A total of 175 aortic grafts were harvested 2 to 90 days after transplantation. Vascular cell apoptosis and CD45+ cell infiltration were significantly reduced in Ad3rsFas-transduced aortas, as compared with control allografts. Moreover, the control allografts developed marked intimal thickening, whereas Ad3rsFas-transduced allografts had significantly less neointima until the 90-day time point.

CONCLUSIONS

sFas overexpression protects the integrity of the vessel wall from immune injury and attenuates transplant arteriosclerosis.

Involvement of the Fas system in liver allograft rejection

OBJECTIVE

Recent studies suggest that apoptosis is an important mechanism of cell death in the rejection of liver allografts and that this process is mediated via Fas. The aim of this study was to analyze the expression of the Fas system during the liver allograft rejection and its evolution after treatment.

METHODS

We evaluated 14 patients with liver allograft rejection before and after treatment. Fas immunostaining was performed by the labeled streptavidin-biotin peroxidase method using a 200-fold dilution of a monoclonal antibody. Assessment of apoptosis was determined by the terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) technique on deparaffined liver samples. Serum levels of soluble Fas antigen (sFas) were detected by an enzyme immunoassay procedure. Twelve liver transplant patients without allograft rejection were analyzed as a control group.

RESULTS

The number of hepatocytes expressing Fas antigen, the percentage of apoptotic hepatocytes, and the sFas levels were higher in patients with liver allograft rejection than in controls (27.9+/-23.1% vs 1.4+/-1.2%, p < 0.001; 2.2+/-0.9% vs 1.0+/-0.1%, p = 0.02; 24.2+/-39.6 vs 2.8+/-4.0 IU/ml, p = 0.03, respectively). There was a correlation between the levels of sFas, AST (r = 0.86, p < 0.001), ALT (r = 0.78, p = 0.02), and gamma-globulin levels (r = 0.86, p < 0.001). After the rejection treatment we found a significant decrease in the Fas antigen expression (18.6+/-13.3%, p < 0.05), TUNEL index (0.2+/-0.4, p < 0.05), and levels of sFas (9.9+/-30.25 IU/ml, p = 0.005).

CONCLUSIONS

1) The demonstration of hepatocytes with Fas antigen expression and the labeling of the nuclei by the TUNEL assay suggest that apoptosis mediated by the Fas system plays a role in the pathogenesis of liver allograft rejection. 2) The Fas expression and the sFas levels decreased in patients with treatment response.

Zinc chloride-mediated reduction of apoptosis as an adjunct immunosuppressive modality in cardiac transplantation

BACKGROUND

Zinc (Zn) blocks caspase-3 activation in cardiac allografts and therefore may synergistically decrease apoptosis along with cyclosporine (CsA), which inhibits mitochondrial release of cytochrome c. Simultaneous treatment of rat recipients of heterotopic heart transplants with zinc chloride (ZnCl(2)) thus may allow lower doses of CsA for immunosuppression.

METHODS

PVG (RT1(c)) rat hearts were transplanted heterotopically into the abdomen of ACI (RT1(a)) rats. Group 1 (n = 15) rats received no treatment. Group 2 rats (n = 8) received 2 mg/kg/day CsA (sub-therapeutic dose) by oral gavage. Group 3 rats (n = 9) received 2 mg/kg/day oral CsA in addition to 1 mg/kg/day sub-cutaneous ZnCl(2) delivered by osmotic pump. All rats were imaged using Annexin V-bound (99m)Technetium ((99m)Tc-Annexin V) on post-operative Day 4 and subsequently killed. Annexin V avidly binds apoptotic cells in vivo. Region of interest per whole body (WB) data were calculated using the images. The allograft survival study was conducted with n = 11, 6, and 5 in control, CsA, and CsA+Zn groups, respectively. Finally, percentages of allografts that reached tolerance were measured in both CsA-only and CsA+Zn groups (n = 8 each).

RESULTS

Zinc chloride had an additive effect with CsA on apoptotic blockade and graft survival. The regions of interest per WB uptake of (99m)Tc-Annexin V were 2.43% +/- 0.37%, 2.08% +/- 0.52%, and 1.49% +/- 0.29%*, and acute survivals were 6.4 +/- 1.7, 7.2 +/- 2.1, and 11.2 +/- 2.5* days for control, CsA, and CsA+Zn groups, respectively (*p < 0.001 vs controls). In addition, 87.5% of allografts became tolerant and survived for 90 days in the CsA+Zn group compared with only 37.5% in the CsA-only group (p = 0.049).

CONCLUSION

Zinc-mediated reduction of apoptosis served as an effective adjunct immunosuppressive therapy to CsA in a rat model of cardiac transplantation.

TGF-beta1 and donor dendritic cells are common key components in donor-specific blood transfusion and anti-class II heart graft enhancement, whereas tolerance induction also required inflammatory cytokines down-regulation

Heart allograft tolerance in adult recipients can be induced in the LEW.1W to LEW.1A congeneic strain combination by pre-graft donor-specific blood transfusion (DST). Long-term survivors accept LEW.1W graft but reject third party skin grafts. As tolerant recipients of heart allografts showed an increase in anti-donor class II antibodies, we hypothesize that these antibodies could be instrumental in tolerance induction. However, anti-donor MHC class II alone prolonged graft survival but did not induce heart allograft tolerance in this combination. We analyzed the immune response patterns in heart allograft recipients following the injection of anti-donor class II antibodies (prolongation) or DST priming (tolerance). As suggested by the different phenomena, several immunological patterns were strikingly different between the two models. In strong contrast to DST-tolerant recipients, at 5 days after transplantation, neither Th1/Th2 nor inflammatory cytokines were inhibited in recipients treated with anti-donor class II antibodies, in which only prolongation of graft survival was induced. Nevertheless, in both models, depletion of resident dendritic cells (DC) from donor hearts inhibited tolerance induction (DST) or shortened allograft survival (anti-donor class II antibodies). Moreover, TGF-beta1 was not down-regulated and administration of neutralizing anti-TGF-beta1 antibody, which inhibited tolerance induction (DST), also shortened allograft survival (anti-donor class II antibodies). These results suggest that, in these two MHC class II-restricted models, both TGF-beta1 and donor DC have a pivotal role in prolonging graft survival. However, in the days following transplantation, further inhibition of inflammatory cytokine production, particularly Th1 and macrophage-derived cytokines is required for tolerance induction.

sTNFRI and sTNFRII synthesis by fine-needle aspiration biopsy sample cultures is significantly associated with acute rejection in kidney transplantation

BACKGROUND

Previously we reported that cultures of fine-needle aspiration biopsy (FNAB) samples synthesize different cytokine pattern depending on the alloimmune response towards the kidney graft. However, we failed to find a clear picture for growth factors implicated in early T-cell activation (interferon-gamma, interleukin [IL]-4, IL-12), although we observed that interleukin-1 receptor antagonist (IL-1ra) was associated with absence of acute rejection. We have now studied tumor necrosis factor-alpha (TNF-alpha) and its two soluble receptors, sTNFRI and sTNFRII, IL-1beta and soluble IL-1 receptor II (sIL-1RII), and leukemia inhibitory factor (LIF), all potential modulators of T-cell activation.

METHODS

Sixty-six cadaver kidney transplants (KTX) were divided into four groups: group 1, day 7 after KTX, stable (n=30); group 2, day 7 after KTX, 8+/-4.5 days before acute rejection (n=12); group 3, first day of acute rejection (n=17); and group 4, day 14 after KTX, stable (n=32). Patients from groups 1 and 4 remained rejection-free for the first 6 months. All rejection episodes were confirmed by core renal biopsy. FNAB samples were cultured according to our published methodology, and culture supernatants were collected at 48 hr and analyzed by ELISA for IL-1beta, sIL-1RII, TNF-alpha, sTNFRI, sTNFRII, and LIF. Serum levels for sIL-1RII, sTNFRI, and sTNFRII were also measured.

RESULTS

FNAB cultures from groups 1 and 4 synthesized significantly lower amounts of sTNFRI and sTNFRII than those from either groups 2 or 3. Both sTNFRI and sTNFRII reached high positive and negative predictive values for acute rejection. IL-1beta and sIL-1RII were synthesized by all groups but without differences. No trace of LIF and TNF-alpha was found. sTNFRII was significantly higher in serum from group 3.

CONCLUSIONS

Both TNF receptors were positively associated with acute rejection and were good predictors of impending acute rejection. The ratio of sIL-1RII over IL-1 (together with IL-1ra that we previously measured in FNAB cultures) suggests that IL-1 actions may be inhibited with current immunosuppression early after transplantation.

Lethal hepatitis after gene transfer of IL-4 in the liver is independent of immune responses and dependent on apoptosis of hepatocytes: a rodent model of IL-4-induced hepatitis

The putative role of IL-4 in human and animal models of hepatitis has not yet been directly determined. We now report that direct expression of IL-4 in the liver of rats or mice using recombinant adenoviruses coding for rat or mouse IL-4 (AdrIL-4 and AdmIL-4, respectively) results in a lethal, dose-dependent hepatitis. The hepatitis induced by IL-4 was characterized by hepatocyte apoptosis and a massive monocyte/macrophage infiltrate. IL-4-induced hepatitis was independent of T cell-mediated immune responses. Hepatitis occurred even after gene transfer of IL-4 into nude rats, CD8-depleted rats, cyclosporine A-treated rats, or recombinase-activating gene 2(-/-) immunodeficient mice. Peripheral depletion of leukocytes using high doses of cyclophosphamide, and/or the specific depletion of liver macrophages with liposome-encapsulated dichloromethylene diphosphonate in rats did not block lethal IL-4-induced hepatitis. Direct transduction of hepatocytes with adenoviruses was not essential, since injection of AdrIL-4 into the hind limb induced an identical hepatitis. Finally, primary rat hepatocytes in culture also showed apoptosis when cultured in the presence of rIL-4. IL-4-dependent hepatitis was associated with increases in the intrahepatic levels of IFN-gamma, TNF-alpha, and Fas ligand. Administration of AdmIL-4 to IFN-gamma, TNF-alpha receptor type I, or TNF-alpha receptor type II knockout mice also resulted in lethal hepatitis, whereas a moderate protection was observed in Fas-deficient lpr mice. IL-4-dependent hepatocyte apoptosis could be abolished by treatment with caspase inhibitory peptides. Our results thus demonstrate that IL-4 causes hepatocyte apoptosis, which is only partially dependent on the activation of Apo-1-Fas signaling and is largely independent of any immune cells in the liver.

A serine protease inhibitor, N-alpha-tosyl-l-lysine chloromethyl ketone, prolongs rat hepatic allograft survival

BACKGROUND

Serine protease inhibitors have profound suppressive effects on cellular and humoral immune responses. We investigated the effect of a serine protease inhibitor, N-alpha-tosyl-l-lysine chloromethyl ketone (TLCK), on hepatic allograft survival in rats. Methods. Orthotopic hepatic transplantation was performed in an ACI (RT1(a))-to-LEW (RT1(1)) rat combination. TLCK was administered continuously at a dose of 4.4 mg/kg/day using an osmotic subcutaneous infusion minipump.

RESULTS

TLCK prolonged hepatic allograft survival. Histologic staging of acute rejection based on Banff criteria in TLCK-treated hepatic allografts was significantly lower than in untreated allografts. TLCK significantly reduced serum concentrations of interferon (IFN)-gamma and tumor necrosis factor (TNF) alpha in allograft recipients. TNF-alpha mRNA levels in TLCK-treated allografts were significantly lower than in untreated allografts. TLCK also decreased perforin mRNA levels in hepatic allografts. Hepatic infiltrates eluted from TLCK-treated allografts showed significantly lower cell-mediated lympholytic activity against donor Con A blast cervical lymph node cells than those from untreated allografts. In vitro, TLCK suppressed interleukin-2 production and [(3)H]thymidine incorporation into an allogeneic mixed lymphocyte reaction.

CONCLUSION

TLCK suppressed acute allograft rejection, suggesting a novel immunosuppressive strategy for therapy of acute organ rejection.

CORRELATION OF FAS AND FAS LIGAND EXPRESSION WITH REJECTION STATUS OF TRANSPLANTED HEART IN HUMAN1

BACKGROUND

Activation of pro-apoptotic systems has been proven in rejection model of animal heart transplantation. The role of Fas and Fas ligand (FasL) in graft rejection is not fully understood, and the expression changes of these genes in human transplanted heart have not been elucidated.

METHODS

Endomyocardial biopsy samples were taken from 13 consecutive patients undergoing heart transplantation at various times, and they were classified into rejection (REJ, grade 3A or more) and lack of rejection (TOL, grade 1B or less) by International Society of Heart and Lung Transplantation rejection grade. Semiquantitative reverse transcription-polymerase chain reaction and immunohistochemistry were performed to evaluate the status of Fas and FasL expression in each sample.

RESULTS

Fas was constitutively expressed both in REJ and TOL specimens (expression levels normalized by glyceraldehyde-3-phosphate dehydrogenase expression in semiquantitative reverse transcription-polymerase chain reaction of REJ vs. TOL, 0.842+/-0.096 vs. 0.848+/-0.103, P=0.776); however, FasL expression was detected in 66% of REJ samples and 40% of TOL samples. Normalized levels of FasL expression were 0.591+/-0.494 (REJ) and 0.383+/-0.507 (TOL) (P<0.05). FasL was expressed by cardiomyocytes as well as graft-infiltrating cells.

CONCLUSIONS

This up-regulation of FasL may be one of possible mechanisms of apoptosis in rejection process of human cardiac allograft.

FasL is important in costimulation blockade-resistant skin graft rejection

BACKGROUND

Simultaneous blockade of the CD40 and CD28 costimulatory pathways is effective in prolonging allograft survival in murine and primate models. Recent data suggest that intact apoptotic pathways are crucial for the induction of hyporesponsiveness by costimulation blockade. We have studied the impact of fas/fasL signaling, an important T cell apoptotic pathway, on the effects of costimulation blockade. Methods. Wild type, lpr (fas deficient), and gld (fasL deficient), mice were used as donors and recipients in the murine skin graft model. Allograft survival was compared in untreated and costimulation blockade (500 microg anti-CD40L and 500 microg CTLA4-Ig, days 0, 2, 4, 6) treated recipients. In some recipients, CD4+ T cells were depleted using rat anti-murine CD4 (100 microg day -3, -2, -1, and weekly).

RESULTS

gld mice treated with costimulation blockade enjoy a significantly greater increase in skin allograft survival than do wild-type mice. This effect is not replicated using lpr donors or recipients. Experiments in which CD4+ cells were depleted demonstrate that fasL is not necessary for CD8-mediated allograft rejection, and that depletion of CD4+ cells eliminates some of the survival advantage induced by costimulation blockade.

CONCLUSIONS

FasL is not required for the establishment of costimulation blockade induced hyporesponsiveness, but rather appears to be required for normal costimulation blockade resistant rejection. Fas expression is not critical for costimulation blockade resistant rejection, suggesting that fasL may be interacting with other receptors. Further, it appears that CD4+ cells are important in the maintenance of allograft protection induced by costimulation blockade in this model.

Activation of the heart by donor brain death accelerates acute rejection after transplantation

BACKGROUND

Donor brain death upregulates expression of inflammatory mediators in the heart. It is hypothesized that these nonspecific changes trigger and amplify acute rejection in unmodified recipients compared with hearts from normal living donors. We examined the inflammatory and immunological consequences of gradual-onset donor brain death on cardiac allografts after transplantation.

METHODS AND RESULTS

Functioning hearts were engrafted from normotensive donors after 6 hours of ventilatory support. Hearts from brain-dead rats (Fisher, F344) were rejected significantly earlier (mean+/-SD, 9. 3+/-0.6 days) by their (Lewis) recipients than hearts from living donor controls (11.6+/-0.7 days, P=0.03). The inflammatory response of such organs was accelerated, with rapid expression of cytokines, chemokines, and adhesion molecules and brisk infiltration of associated leukocyte populations. Upregulation of major histocompatibility class II antigens increased organ immunogenicity. Acute rejection evolved in hearts from brain-dead donors more intensely and at a significantly faster rate than in controls.

CONCLUSIONS

Donor brain death is deleterious to transplanted hearts. The resultant upregulation of inflammatory factors provokes host immune mechanisms and accelerates the acute rejection process in unmodified hosts.

Reduction of liver Fas expression by an antisense oligonucleotide protects mice from fulminant hepatitis

Aberrant apoptosis-mediated cell death is believed to result in a number of different human diseases. For example, excessive apoptosis in the liver can result in fulminant and autoimmune forms of hepatitis. We have explored the possibility that inhibition of Fas expression in mice would reduce the severity of fulminant hepatitis. To do this, we have developed a chemically modified 2'-O-(2-methoxy)ethyl antisense oligonucleotide (ISIS 22023) inhibitor of mouse Fas expression. In tissue culture, this oligonucleotide induced a reduction in Fas mRNA expression that was both concentration- and sequence-specific. In Balb/c mice, dosing with ISIS 22023 reduced Fas mRNA and protein expressions in liver by 90%. The ID50 for this response was 8-10 mg kg-1 daily dosing, and the reduction was highly dependent on oligonucleotide sequence, oligonucleotide concentration in liver, and treatment time. Pretreatment with ISIS 22023 completely protected mice from fulminant hepatitis induced by agonistic Fas antibody, by a mechanism entirely consistent with an oligonucleotide antisense mechanism of action. In addition, oligonucleotide-mediated suppression of Fas expression reduced the severity of acetaminophen-mediated fulminant hepatitis, but was without effect on concanavalin A-mediated hepatitis. Our results demonstrate that 2'-O-(2-methoxy)ethyl containing antisense oligonucleotides targeting Fas can exert in vivo pharmacological activity in liver, and suggest that oligonucleotide inhibitors of Fas may be useful in the treatment of human liver disease.

Prolonged survival of heart allografts from p53-deficient mice

BACKGROUND

Acute rejection of the heart allograft is the major cause of heart failure in the first month after transplantation. Most studies on the prevention of acute rejection have concentrated on immune suppression of the recipients, whereas little is known about the effects of genetically manipulated donor organs on heart allograft survival. Herein, we describe a mouse model of heart allografts donated by p53-/- mice that can prolong the survival time of the grafts.

METHODS

Hearts of p53-/- or p53+/+ C57BL/6J mice were grafted to the neck carotid artery and jugular vein of BALB/c mice using a cuff technique. The graft survival was observed daily. The hearts were analyzed using several techniques, including histology, immunofluorescence, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), and Western blot analysis.

RESULTS

p53+/+ allografts ceased beating at 7.6+/-0.5 days, whereas p53-/- hearts were beating at 10.5+/-1.1 days after transplantation (P<0.01). Mean histological rejection scores were significantly lower in allografts donated by p53-deficient mice. Furthermore, apoptotic cells, determined by TUNEL and a reagent kit for detection of cardiac apoptosis, were of high numbers in the allograft sections from wild-type hearts but rare in p53-/- allografts (4.2+/-1.3 vs. 0.7+/-0.5/250x field). Immunofluorescence staining and Western blot analysis revealed that high levels of p53 and proapoptotic protein Bax were expressed in wild-type grafts but not p53-/- allografts. Interestingly, Bcl-2, an antiapoptotic protein, was abundant in cardiac allografts from p53-/- mice and almost undetectable in grafts from wild-type mice.

CONCLUSIONS

Thus, p53 is involved in cardiac apoptosis induced by alloimmune reaction, and prolonged survival of heart allografts can be achieved when p53 is lacking.

Acute cellular rejection of human renal tissue by adoptive transfer of allogeneic human peripheral blood mononuclear cells into chimeric rats: sequential gene expression of cytokines, chemokines and cytolytic effector molecules, and their regulation by CTLA-4-Ig

T(h)1- and T(h)2-related cytokines (IFN-gamma, IL-2, IL-4, IL-10), beta-chemokines (RANTES, macrophage inflammatory protein-1beta) and their receptor [chemotatic cytokine receptor (CCR) 5], and the cytolytic effector molecule [Fas ligand (FasL)] play an essential role in regulating and co-ordinating acute renal allograft rejection. A chimeric model of acute cellular rejection which involves subcapsular grafting of human renal tissue in the kidneys of immunodeficient rats and subsequent i.p. infusion of allogeneic human peripheral blood mononuclear cells (PBMC) was used to study cellular infiltration patterns and sequential intragraft gene expression of these key inflammatory mediators. We found that while all molecules are expressed within the human renal implant at specific time points following infusion of allogeneic human PBMC, peak mRNA expression of IFN-gamma, IL-2, RANTES and CCR5 is associated with a phase of human mononuclear infiltration and accumulation, prior to graft destruction (induction phase). A short burst of FasL gene expression is found at the end of induction and at the onset of graft deterioration. IL-4 mRNA, which is hardly detectable, and IL-10 mRNA, which appears early and persists throughout follow-up at high levels, both peak after the induction phase with the advent of graft destruction. Furthermore, treatment with CTLA-4-Ig, which hardly affects migration of human effector cells into graft tissue, is associated with a temporary reduction in gene transcript levels for all inflammatory mediators, especially IL-2 and IL-4, reduced apoptosis in the graft and amelioration of tissue injury. Thus, development of acute cellular rejection in our chimeric model involves a co-ordinated pattern of gene expression, in which CTLA-4-Ig promotes its effects by transient inactivation of infiltrating human cells.

Alloantibody-Mediated Class I Signal Transduction in Endothelial Cells and Smooth Muscle Cells: Enhancement by IFN-γ and TNF-α

Chronic rejection is the major limiting factor to long term survival of solid organ allografts. The hallmark of chronic rejection is transplant atherosclerosis, which is characterized by the intimal proliferation of smooth muscle cells, endothelial cells, and fibroblasts, leading to vessel obstruction, fibrosis, and eventual graft loss. The mechanism of chronic rejection is poorly understood, but it is suspected that the associated vascular changes are a result of anti-HLA Ab-mediated injury to the endothelium and smooth muscle of the graft. In this study we have investigated whether anti-HLA Abs, developed by transplant recipients following transplantation, are capable of transducing signals via HLA class I molecules, which stimulate cell proliferation. In this report we show that ligation of class I molecules with Abs to distinct HLA-A locus and HLA-B locus molecules results in increased tyrosine phosphorylation of intracellular proteins and induction of fibroblast growth factor receptor expression on endothelial and smooth muscle cells. Treatment of cells with IFN-γ and TNF-α up-regulated MHC class I expression and potentiated anti-HLA Ab-induced fibroblast growth factor receptor expression. Engagement of class I molecules also stimulated enhanced proliferative responses to basic fibroblast growth factor, which augmented endothelial cell proliferation. These findings support a role for anti-HLA Abs and cytokines in the transduction of proliferative signals, which stimulate the development of myointimal hyperplasia associated with chronic rejection of human allografts.

Recombinant IFN-gamma abrogates allograft tolerance induced by donor-specific blood transfusion by restoring alloantibody production

Donor-specific tolerance to heart allograft was induced in adult Lewis rats by pregraft donor-specific blood transfusion (DST). We previously showed that this tolerant state is characterized by a dramatic inhibition of T cell and macrophage activation. In addition, tolerant animals could not mount an efficient anti-donor humoral response whereas transfer of sera from rejecting animals triggered rejection in tolerant animals. This tolerance can be abrogated by daily post-graft administration of recombinant IFN-gamma (rIFN-gamma). To elucidate the mechanisms of action of rIFN-gamma, T cell, macrophage and B cell functions were assessed in allograft recipients. IFN-gamma did not restore the expression of Th1-related cytokine mRNA or the activated macrophage product inducible nitric oxide synthase in allografts. Importantly, rIFN-gamma treatment promptly restored the anti-donor humoral response in DST-treated recipients. We conclude that rIFN-gamma treatment in DST-treated allograft recipients cannot reverse the unresponsive state of Th1 cells and macrophages infiltrating the graft, but can provide B cell help for IgG alloantibody production which is lacking in these animals.

A critical role for transforming growth factor-beta in donor transfusion-induced allograft tolerance

Donor-specific (DST) or nonspecific blood transfusions administered before transplantation can enhance survival of vascularized allografts both in humans and animals but the immunological mechanisms of this effect remain unclear. We have analyzed the expression and the role of endogenous TGF-beta1 in a model of heart allograft tolerance, induced by pregraft DST in adult rats. We reported previously that this tolerance occurs despite a strong infiltration of leukocytes into the graft that are unable to produce both Th1- and Th2-related cytokines in vivo. Allografts from DST-treated rats express high levels of TGF-beta1 mRNA and active protein. This phenomenon is correlated with the rapid infiltration of leukocytes producing high amounts of TGF-beta1. TGF-beta1-producing cells are virtually absent among early infiltrating cells in rejected grafts but are found at a later time point. The induction of allograft tolerance in vivo is abrogated by administration of neutralizing anti-TGF-beta mAb. Moreover, overexpression of active TGF- beta1 in heart allografts using a recombinant adenovirus leads to prolonged graft survival in unmodified recipients. Taken together, our results identify TGF-beta as a critical cytokine involved in the suppression of allograft rejection induced by DST and suggest that TGF-beta-producing regulatory cells are also involved in allograft tolerance.