Prolonged survival of rat liver allografts transfected with Fas ligand-expressing plasmid

High expression of Fas ligand on cord blood dendritic cells: a possible immunoregulatory mechanism after cord blood transplantation

BACKGROUND

Allogeneic cord blood transplantation is associated with less severe graft-versus-host disease (GVHD). Dendritic cells (DCs), as the most potent antigen-presenting cells of the immune system, play a central role in the development of GVHD. Because apoptosis induction is one of the known mechanisms that DCs use to regulate T-cell responses, we studied the immunostimulatory and apoptosis induction capacities of cord blood dendritic cells (CBDCs) and peripheral blood dendritic cells (PBDCs) to evaluate the mechanisms underlying the lower incidence of GVHD after cord blood transplantation. Presence of apoptosis-related markers Fas, Fas ligand (FasL), and CD40 and costimulatory molecules, along with the proportion of myeloid and lymphoid DCs subsets, were also measured on CBDCs and PBDCs.

METHODS

Fresh CBDCs and PBDCs were isolated from cord and peripheral mononuclear cells as lineage-negative cells by using monoclonal antibodies against CD3, CD11b, CD14, CD16, CD19, CD56, CD34, and CD66b. DCs were cocultured with allogeneic T cells, and the effect of CBDCs and PBDCs on T-cell apoptosis and proliferation were determined through flow cytometric analysis and 3H-thymidine incorporation.

RESULTS

Our findings showed that CBDCs markedly augment apoptosis of CD3+ T-cells. FasL expression on CBDCs was significantly higher than on PBDCs. However, there was no difference between Fas expression on CBDCs and PBDCs. Moreover, CBDCs were poor stimulators of allogenic T cells in mixed leukocyte reaction compared with adult peripheral blood DCs. They also displayed decreased expression of HLA-DR and CD86 molecules. The ratio of lymphoid DCs (CD11c-, CD123+) to myeloid DCs (CD11c+, CD123-) was also significantly higher in CBDCs compared with PBDCs.

CONCLUSIONS

It seems that less severe GVHD after cord blood transplantation is due not only to a higher degree of immaturity of CBDCs, but also to delivery of apoptotic signals to the host T cells that recognize allo-MHC molecules on CBDCs in the early phase of immune response.

Gene therapy in transplantation

Gene therapy is an exciting and novel technology that offers the prospect of improving transplant outcomes beyond those achievable with current clinical protocols. This review explores both the candidate genes and ways in which they have been deployed to overcome both immune and non-immune barriers to transplantation success in experimental models. Finally, the major obstacles to implementing gene therapy in the clinic are considered.

Fas ligand exerts its pro-inflammatory effects via neutrophil recruitment but not activation

Fas ligand (FasL) expression induces apoptosis of activated T cells and has been suggested as a strategy to inhibit graft rejection. Unfortunately, the use of FasL to confer 'immune privilege' in this setting has been hampered by the finding that it may also provoke a destructive granulocytic response. While the Fas/FasL-mediated apoptotic pathways are well defined, the pro-inflammatory effects of FasL are poorly understood. Our aim in this study was to define in vitro the biological effects of FasL on neutrophil recruitment and activation. DAP-3 cells expressing human FasL on the cell membrane (mFasL) potently induced apoptosis in human neutrophils and in activated T lymphocytes. Recombinant human soluble FasL (sFasL), by contrast, was a very weak inducer of apoptosis, even at high concentrations. This latter observation suggests that cleavage of mFasL by naturally occurring matrix metalloproteinases may serve to down-regulate FasL activity in vivo. However, in the presence of a cross-linking antibody, the efficiency of apoptosis-induction by sFasL was greatly increased, suggesting that the lesser pro-apoptotic potency of sFasL reflects an inability to induce trimerization of the Fas receptor. With regard to pro-inflammatory effects, we found that sFasL is a potent neutrophil chemoattractant and, given that it induces little apoptosis, the dominance of sFasL over mFasL may mean that graft-infiltrating neutrophils will survive to mediate inflammation. Neither sFasL nor mFasL produced neutrophil activation as assessed by chemiluminescence assay. This suggests that neutrophils recruited to an inflammatory site by FasL will be activated by mechanisms other than Fas-FasL signalling.

The role of death receptor ligands in shaping tumor microenvironment

Death receptor ligands (FasL, TRAIL) activate apoptosis in cells expressing the cognate receptors. Evidence suggests that these ligands also deliver pro-inflammatory signals. In the tumor microenvironment, "Fas counterattack" mounted by tumors against immune cells is mediated by tumor-associated FasL. But death ligands crosslinking their receptors also induce inhibition of apoptosis and activation of the transcription factor, NFkappaB, with a subsequent burst of pro-inflammatory cytokine production and tumor growth promotion. NFkappaB, a key link between inflammation and cancer, regulates dual activities of death ligands, depending on molecular signals in the tumor microenvironment. This paper focuses on death ligands as an example of the extensive repertoire of strategies devised by tumors for escape from immune control.

Exogenous Expression of Fas-Ligand or CrmA Prolongs the Survival in Rat Liver Transplantation

Modulation of donor organs by transfection of a gene encoding immmunosuppresive molecules has been recognized as a less toxic approach to prevent allograft rejection. Fas-ligand (FasL) plays a critical role in activation-induced cell death of activated cytotoxic lymphocytes. This may provide a potential for induction of "immune privileged sites" to escape the host immune surveillance system. Cytokine response modifier A (CrmA), a gene product of cowpox virus, blocks caspase as well as perforin/granzyme-mediated apoptotic pathways. Therefore, it may suppress intragraft apoptosis. The aim of the present study was to investigate whether transfection of FasL or CrmA genes prolonged the survival of rat liver allografts. Using the high responder rat combination of DA (RT-1(a)) donor to LEW (RT-1(1)) recipient, we performed orthotopic liver transplantation with subsequent delivery of adenoviral vectors containing FasL, CrmA, or LacZ, at a dose of 1 x 10(9) pfu via a recipient tail vein using a Cre-mediated gene expression system. Recipient survival was assessed as well as immunohistochemical examination of the grafts for anti-CD2, TUNEL, and H&E staining. Statistical analysis was performed with the Mann-Whitney U test. The therapeutic groups showed significantly prolonged recipient survival compared with the LacZ-treated control group. Histologic analysis revealed reduced hepatocyte apoptosis in the CrmA-treated group and increased apoptosis of infiltrating mononuclear cells in the FasL-treated group. These data suggested that FasL and CrmA may be potent genes to prolong rat liver allograft survival.

Genetic Heterogeneity and Efficiency of Two Different Methods of Adenovirus-Mediated Gene Transfer in a Rat Liver Transplantation Model

PURPOSE

We used recombinant adenoviral vectors for gene therapy in liver transplantation, and investigated the efficacy of gene transfer and expression on the grafts and genetic heterogeneity, with two exogenous gene transfer methods in three different syngeneic rat strains.

METHODS

We transferred adenoviral vector encoding Escherichia coli beta-galactosidase via a donor tail vein 3 days before transplantation; via a recipient tail vein immediately after grafting; and ex vivo by perfusion and clamping during transplantation.

RESULTS

The high efficacy of beta-galactosidase gene transfer and expression was seen in both delivery systems, with 70% positivity for hepatocytes on day 3, which persisted for at least 3 weeks after transplantation. The efficacy of gene transfer and expression was similar in the three strains (DA, Lewis, and PVG).

CONCLUSIONS

These data suggest that adenovirus-mediated gene transfer delivers effective gene therapy by tail vein injection of a donor or a recipient, or by ex vivo graft perfusion in rat liver transplantation. It is not necessary to consider the differences in the strains. Furthermore, ex vivo graft perfusion is probably more suitable not only for rat liver transplantation but also possibly for future clinical application.

Fas ligand expression in human and mouse cancer cell lines; a caveat on over-reliance on mRNA data

Background

During carcinogenesis, tumors develop multiple mechanisms for evading the immune response, including upregulation of Fas ligand (FasL/CD95L) expression. Expression of FasL may help to maintain tumor cells in a state of immune privilege by inducing apoptosis of anti-tumor immune effector cells. Recently this idea has been challenged by studies reporting that tumor cells of varying origin do not express FasL. In the present study, we aimed to comprehensively characterize FasL expression in tumors of both murine and human origin over a 72 hour time period.

Methods

RNA and protein was extracted from six human (SW620, HT29, SW480, KM12SM, HCT116, Jurkat) and three mouse (CMT93, CT26, B16F10) cancer cell lines at regular time intervals over a 72 hour time period. FasL expression was detected at the mRNA level by RT-PCR, using intron spanning primers, and at the protein level by Western Blotting and immunofluorescence, using a polyclonal FasL- specific antibody.

Results

Expression of FasL mRNA and protein was observed in all cell lines analysed. However, expression of FasL mRNA varied dramatically over time, with cells negative for FasL mRNA at many time points. In contrast, 8 of the 9 cell lines constitutively expressed FasL protein. Thus, cells can abundantly express FasL protein at times when FasL mRNA is absent.

Conclusion

These findings demonstrate the importance of complete analysis of FasL expression by tumor cells in order to fully characterize its biological function and may help to resolve the discrepancies present in the literature regarding FasL expression and tumor immune privilege.

The efficacy and safety of gene transfer into the porcine liver in vivo by HVJ (Sendai virus) liposome

BACKGROUND

Gene transfer systems using viral vectors are efficient; however, most viral vectors also tend to evoke immunologic reactions, thereby clinically causing serial side effects. HVJ-liposome vector is a hybrid vector consisting of liposome and an inactivated Sendai virus (Hemmagglutinating Virus of Japan [HVJ]), which has been reported to be less immunogenic and can also be repeatedly administered. We examined the usefulness of this vector for hepatic gene therapy in a pig model.

METHODS

Genes encoding beta-galactosidase and luciferase were used as reporter genes. The pigs were injected with the reporter gene loaded-HVJ-liposome into the portal vein under total vascular exclusion of the liver. The transfection efficiencies were then assessed by beta-galactosidase staining, a luciferase assay, and RT-PCR for LacZ mRNA. Biochemical and histologic analyses were performed to evaluate tissue toxicity after gene transfer.

RESULTS

The luciferase gene expression in the liver reached its highest level at 7 days after transfection. It continued to be detected up to 28 days after transfection, while all pigs remained healthy throughout the observation period. The transfection efficiency was 15% in the hepatocytes according to beta-galactosidase staining. Extrahepatic transgene expression was slightly observed in the lung and kidney, but not in the spleen or ovary.

CONCLUSIONS

These data suggest for the first time that the use of the HVJ-liposome vector is a safe and feasible modality for liver-directed gene transfer in pigs, and it might therefore be suitable for clinical gene therapy trials.

Addressing the "Fas counterattack" controversy: blocking fas ligand expression suppresses tumor immune evasion of colon cancer in vivo

Fas ligand (FasL/CD95L) is a transmembrane protein belonging to the tumor necrosis factor superfamily that can trigger apoptotic cell death following ligation to its receptor, Fas (CD95/APO-1). Expression of FasL may help to maintain tumor cells in a state of immune privilege by inducing apoptosis of antitumor immune effector cells-the "Fas counterattack." However, the ability of FasL to mediate tumor immune privilege is controversial due to studies that indicate FasL has both pro- and anti-inflammatory activities. To resolve this controversy and functionally define the role of FasL in tumor immune evasion, we investigated if suppression of endogenously expressed FasL in colon tumor cells resulted in reduced tumor development and improved antitumor immune challenge in vivo. Specifically, FasL expression in CMT93 colon carcinoma cells was down-regulated following stable transfection with a plasmid encoding antisense FasL cDNA. Down-regulation of FasL expression had no effect on tumor growth in vitro but significantly reduced tumor development in syngeneic immunocompetent mice in vivo. Tumor size was also significantly decreased. Reduced FasL expression by tumor cells led to increased lymphocyte infiltration. The overall level of neutrophils present in all of the tumors examined was low, with no difference between the tumors, irrespective of FasL expression. Thus, down-regulation of FasL expression by colon tumor cells results in an improved antitumor immune challenge in vivo, providing functional evidence in favor of the "Fas counterattack" as a mechanism of tumor immune evasion.

Tumor counterattack: fact or fiction?

Cancer development relies on a variety of mechanisms that facilitate tumor growth despite the presence of a functioning immune system. Understanding these mechanisms may foster novel therapeutic approaches for oncology and organ transplantation. By expression of the apoptosis-inducing protein CD95L (FasL, APO-1L, CD178), tumors may eliminate tumor-infiltrating lymphocytes and suppress anti-tumor immune responses, a phenomenon called "tumor counterattack". On the one hand, preliminary evidence of tumor counterattack in human tumors exists, and CD95L expression can prevent T-cell responses in vitro. On the other hand, CD95L-expressing tumors are rapidly rejected and induce inflammation in mice. Here, we summarize and discuss the consequences of CD95L expression of tumor cells and its contribution to immune escape.

The role of Fas ligand as an effector molecule in corneal graft rejection

Previous studies have shown that the expression of Fas ligand (FasL; CD95L) by donor corneas is critical to their survival when placed on allogeneic recipients. Since there have been reports that the cornea expresses Fas, we tested the idea that FasL on lymphoid cells could be an effector molecule during rejection episodes. When FasL defective BALB/c-gld mice were engrafted with allogeneic corneas, significantly more of these corneas were accepted than by normal BALB/c mice. However, this was not due to impaired FasL-mediated effector function in these mice as the allogeneic corneas did not express detectable Fas by Western blot or RT-PCR analysis. Furthermore, donor corneas without Fas were given no survival advantage, but were rejected similar to wild-type donor allogeneic corneas. Examination of the T cell compartment in gld mice revealed that these cells express higher levels of Fas and are more susceptible to Fas-mediated death than wild-type cells. These results indicate that FasL is not an effector molecule in corneal graft rejection and that gld mice show reduced graft rejection due to greater susceptibility of their T cells to Fas-mediated apoptosis.

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.

Fas Ligand as a Tool for Immunosuppression and Generation of Immune Tolerance

The role of Fas ligand (FasL) in physiologically limiting immune responses and maintaining immune-privileged sites has led to a body of research aiming to confer protection to allogeneic grafts by expressing FasL on the allogeneic tissue or by administrating FasL-transduced donor dendritic cells. In addition, several studies have used FasL to abrogate autoimmune responses. This review presents the results of these studies and discusses the problems associated with FasL usage.

The Fas signalling pathway and its role in the pathogenesis of cancer

Tumor cells frequently exhibit de novo expression of Fas ligand (FasL/CD95L). Coupled with resistance to Fas-mediated apoptosis, FasL expression enables many cancers to deliver a pre-emptive strike or 'counterattack' against the immune system. New studies also indicate that FasL expression on tumor cells could confer a double advantage to these cells by stimulating their own proliferation. However, pro-inflammatory effects of FasL have also been observed. New findings are beginning to reconcile the paradoxical effects of FasL, with the clinical significance of the Fas counterattack only beginning to emerge.

Termination of Antigen-Specific Immunity by CD95 Ligand (Fas Ligand) and IL-10

Following elimination of a foreign invader, the immune system must return to its normal quiescent levels. This process requires removal of reactive immune cells when they are no longer needed. We have explored the role of Fas/Fas ligand (FasL) in terminating immunity and demonstrate that mice defective in these proteins have prolonged immune responses. Studies demonstrate that termination of immunity occurs via the interaction of Fas(+) lymphoid cells with FasL(+) nonlymphoid cells at the site of Ag challenge. Our results also show that FasL is absent in quiescent tissue but is rapidly up-regulated during the local immune reaction. This occurs through the production of IL-10. Thus, FasL and IL-10 work in concert to eliminate inflammatory cells and control the duration of an immune response.

Endothelial overexpression of Fas ligand decreases atherosclerosis in apolipoprotein E-deficient mice

OBJECTIVE

Fas ligand (FasL) can induce apoptosis in cells bearing the Fas receptor. The role of FasL in the vasculature with regard to atherosclerosis is controversial. This study examined the function of endothelial FasL during atherosclerosis.

METHODS AND RESULTS

Transgenic (Tg) mice that specifically overexpress different levels of FasL on vascular endothelial cells were crossed into the apolipoprotein E-knockout background (ApoE-KO) to generate ApoE-KO/FasL-Tg mice. Although plasma cholesterol and triglyceride levels were not different between ApoE-KO/FasL-Tg mice and ApoE-KO mice after 12 weeks of a high-fat diet, overexpression of the FasL transgene significantly reduced atherosclerotic lesion area in aortae by 49%. The reduction of atherosclerotic lesion area was more pronounced in thoracic and abdominal aortae than in the aortic arch, and a 34% reduction in lesion area was observed in aortic root sections from the ApoE-KO/FasL-Tg group compared with the ApoE-KO group. Immunostaining revealed significant decreases in both macrophage and CD8 T-cell accumulation in lesions of ApoE-KO/FasL-Tg mice. ApoE-KO/FasL-Tg mice that express lower levels of endothelial FasL also displayed reduced lesion size, but this reduction was statistically significant at the aortic arch only.

CONCLUSIONS

Overexpression of endothelial FasL is antiinflammatory and inhibits atherosclerosis under hypercholesterolemic conditions.

N/A

N/A

Cell surface expression of MHC class I antigen is suppressed in indoleamine 2,3-dioxygenase genetically modified keratinocytes: implications in allogeneic skin substitute engraftment

Indoleamine 2,3-dioxygenase (IDO) has been indicated to prevent the fetus from maternal T-cell rejection. A longer survival of IDO genetically modified islets transplanted into NOD mouse kidney capsules has also been demonstrated. As IDO mediated mechanism of graft protection has not been elucidated, in our study we hypothesize that the expression of IDO may prevent immune rejection by suppressing the major histocompatibility complex (MHC) class I antigen. To test this hypothesis, an IDO adenoviral vector was constructed and the effect of IDO on MHC class I expression was evaluated on recombinant adenoviral transfected keratinocytes. Following a successful construction of IDO expressing adenoviral vector, the catabolic activity of IDO enzyme was evaluated by measuring the levels of its product, kynurenine in keratinocyte conditioned medium. The results indicated a higher level of kynurenine in IDO expressing cells relative to those of control cells. The results of MHC class I experiments revealed a significant downregulation of cell membrane associated MHC class I antigen in IDO genetically modified keratinocytes relative to that of either nontransfected or empty vector transfected cells. Further experiments demonstrated that an addition of tryptophan or IDO inhibitor markedly restored the expression of MHC class I on IDO transfected keratinocytes. The findings of this study suggest that downregulation of MHC class I expression by IDO might be one of the mechanisms through which IDO mediates local immunosuppression.

Human Fas-ligand expression on porcine endothelial cells does not protect against xenogeneic natural killer cytotoxicity*

Several human leukocyte subsets including natural killer (NK) cells, cytotoxic T lymphocytes (CTL), and polymorphonuclear neutrophils (PMN) participate in cellular immune responses directed against vascularized pig-to-human xenografts. As these leukocytes express the death receptor Fas either constitutively (PMN) or upon activation (NK, CTL), we explored in vitro whether the transgenic expression of Fas ligand (FasL) on porcine endothelial cells (EC) is a valuable strategy to protect porcine xenografts. The porcine EC line 2A2 was stably transfected with human FasL (2A2-FasL) and interactions of 2A2-FasL with human leukocytes were analyzed using functional assays for apoptosis, cytotoxicity, chemotaxis, adhesion under shear stress, and transmigration. FasL expressed on porcine EC induced apoptosis in human NK and T cells, but did not protect porcine EC against killing mediated by human NK cells. 2A2-FasL released soluble FasL, which induced strong chemotaxis in human PMN. Adhesion under shear stress of PMN on 2A2-FasL cells was increased whereas transendothelial migration was decreased. In contrast, FasL had no effect on the adhesion of NK cells but increased their transmigration through porcine EC. Although FasL expression on porcine EC is able to induce apoptosis in human effector cells, it did not provide protection against xenogeneic cytotoxicity. The observed impact of FasL on adhesion and transendothelial migration provides evidence for novel biological functions of FasL.

Fas ligand mediates immune privilege and not inflammation in human colon cancer, irrespective of TGF-beta expression

Many cancers express Fas ligand (FasL/CD95L) in vivo, and can kill lymphoid cells by Fas-mediated apoptosis in vitro. However, overexpression of recombinant FasL in murine tumour allografts revealed a potential antitumour effect of FasL, via recruitment of neutrophils. Transforming growth factor-β1 (TGF-β1) could inhibit these neutrophil-stimulatory effects of FasL. In the present study, we sought to determine directly whether FasL contributes to immune privilege or tumour rejection in human colon cancers in vivo, and whether TGF-β1 regulates FasL function. Serial tumour sections were immunostained for FasL and TGF-β1. Neutrophils and tumour infiltrating lymphocytes (TILs) were detected by immunohistochemistry for lactoferrin and CD45, respectively. Apoptotic TIL were identified by dual staining for TUNEL/CD45. FasL expression by nests of tumour cells was associated with a mean four-fold depletion of TILs (range 1.8–33-fold, n=16, P<0.001), together with a two-fold increase in TIL apoptosis (range 1.6–2.5-fold, n=14, P<0.001), relative to FasL-negative nests within the same tumours. The overall level of neutrophils present in all tumours examined was low (mean 0.3%, n=16), with FasL expression by tumour nests associated with a mean two-fold decrease in neutrophils, irrespective of TGF-β1 expression. Together, our results suggest that tumour-expressed FasL is inhibitory rather than stimulatory towards antitumour immune responses.

Prolonged survival of rat liver allograft with adenoviral gene transfection of human immunodeficiency virus type 1 nef

HIV-1 nef is believed to allow immune evasion by modifying cell surface molecules because of certain mechanisms such as downregulation of the major histocompatibility complex (MHC) class I molecule complex as well as upregulation of FasL. In the present study, we successfully generated a recombinant adenovirus vector containing HIV-1 nef. We detected the expression of nef in liver infected with AxCANef by immune staining and Western blotting, and confirmed its expression as persistent for more than 4 weeks. Furthermore, the surface expression of MHC class I was downregulated in AxCANef-infected hepatic cells. In addition, we also observed nef-induced FasL upregulation of gene-transfected hepatic cells. Using a DA-to-Lewis orthotopic liver transplantation model, we transfected AxCANef to a liver graft to determine whether nef expression could have an effect on recipient survival. AxCANef significantly prolonged recipient survival time (14.5 days) compared with the uninfected group (11 days) (P <.001) and the AxCALacZ-infected group (11 days) (P <.001). Histologic analysis showed reduction in the number of accumulated inflammatory cells and an increase in apoptotic cells in grafts expressing nef. In conclusion, we showed that the nef gene could prolong survival of rat liver allografts, and this result suggested the potential clinical use of its transfection.

Biology of FasL

FasL (CD95L) is a well-known and well-characterized death-inducing ligand. Spontaneous mutations in FasL and its cognate receptor Fas (CD95) have helped understand the role of these molecules in the disease. Once thought to be mainly involved in the homeostasis of immune system, the territory of FasL regulation has been expanded to angiogenesis and tumor progression. Here, we review what is currently known about the role of FasL in many areas of biology.

Display of Fas ligand protein on cardiac vasculature as a novel means of regulating allograft rejection

BACKGROUND

Fas ligand (FasL) is a potent death-inducing molecule with important functions in immune homeostasis and tolerance to self-antigens. The complex biological activities of FasL and its inefficient expression using conventional gene transfer approaches limit its use for immunomodulation to prevent allograft rejection. We have recently generated a chimeric FasL with core streptavidin (SA-FasL) with potent apoptotic activity and designed a novel approach to display it on the surface of several cell types via biotinylation. We herein tested whether SA-FasL can also be displayed on vascular endothelial cells in the heart and examined its effect on graft survival after transplantation into syngeneic and allogeneic hosts.

METHODS AND RESULTS

SA-FasL was efficiently displayed on the vasculature of BALB/c hearts with a half-life of 9 days in vivo. Transplantation of hearts displaying SA-FasL into syngeneic hosts resulted in indefinite graft survival without detectable toxicity to the grafts and hosts. In contrast, transplantation of allogeneic C57BL/10 hearts displaying SA-FasL into BALB/c recipients resulted in graft rejection, but in a delayed fashion as compared with control hearts (mean survival time=17.4+/-5 versus 9.6+/-1 days). Allograft survival was further extended to 21+/-2.6 and 24+/-3 days (P<0.05) by intravenous treatment of graft recipients with 1 dose of SA-FasL-decorated donor splenocytes on days 2 and 6 after transplantation, respectively.

CONCLUSIONS

This study shows for the first time that exogenous proteins can be displayed on the endothelium of solid organs for therapeutic purposes. This approach provides a convenient and rapid means of displaying exogenous proteins on the surface of cells, tissues, and solid organs, with broad research and therapeutic implications.

Genetic modification of cold-preserved renal grafts using HSP70 or bcl-2 HVJ-liposome method

BACKGROUND

We tested the hypothesis that the best time for genetic modification is while the cell viability of the graft is reduced for long-term preservation. The hemagglutinating virus of Japan (HVJ)-liposome method, a nonviral gene transfer technique, was used with a luciferase gene to test the efficacy of protein induction under the critical preservation time. Furthermore, we tested this genetic modification with heat shock protein (HSP) 70 or bcl-2 genes to prevent primary nonfunction (PNF) after long-term preservation.

METHODS

Orthotopic rat renal transplantation (RT) was performed using the cuff technique in the syngeneic combination of Lew (major histocompatible complex, haplotype: RT1(l)). Rat kidney grafts were preserved for 24 or 48 h in University of Wisconsin (UW) or Ringer's lactate solution using HVJ method with the luciferase gene. Rats with gene-transfected kidneys were re-laparotomized 48 h after transplantation to estimate the lack of arterial flow in the graft and killed for histological evaluation of the degree of PNF luciferase intensity assay. Then, two functional genes (HSP70 or bcl-2) were tested for the occurrence of PNF and histological and immunohistochemical analysis of the grafted kidneys preserved for 48 h in the UW solution.

RESULTS

In the kidneys preserved for 24 h, 50% of the Ringer's lactate group had PNF; but all of the UW group had sufficient blood flow. The graft viability was well corrected by the degree of luciferase intensity. The PNF rate was significantly suppressed in the bcl-2 gene-transfer group, and tended to be reduced in the HSP70 group.

CONCLUSIONS

The HVJ-liposome method effectively induced the foreign gene for kidney grafts even in the cold-preservation solution. Induction of bcl-2 or the HSP70 gene reduced the occurrence of PNF in the rat renal graft. The results suggest that gene transfer not only maintains graft viability, but also graft activation.

FasL-transfected endothelial cells decrease the proliferative response of allogeneic PBL

Graft endothelium has a key role in organ transplantation because it regulates graft infiltration by allogeneic activated T cells. Overexpression of death molecules that could induce apoptosis of alloreactive T cells might be an alternative to the immunosuppressive treatment currently used in graft transplantation. Several studies have shown that immune-privileged sites express Fas ligand (FasL) and induce apoptosis of activated T-cells. We propose that endothelial cells engineered to express FasL could inhibit alloreactive T cell-proliferation by inducing apoptosis. An expression vector was constructed with human FasL cDNA and used to transfect an endothelial cell line (ECV304 cells). We demonstrated that FasL-transfected ECV304 cells were effective in inducing apoptosis of Jurkat T cell lymphoma as an agonist anti-Fas antibody. Using a mixed lymphocyte-endothelial cell culture model we observed that FasL-transfected ECV304 cells which conserved their two principal costimulatory pathways inhibited alloreactive T cell-proliferation by inducing activated T-cell apoptosis. These results suggest that endothelial cells could be interesting candidates to convey a death signal and induce hyporesponsiveness of alloreactive T cells during organ transplantation.

Cloning and potential utility of porcine Fas ligand: overexpression in porcine endothelial cells protects them from attack by human cytolytic cells

Endothelial cells (EC) are primary targets of the recipient's immune response to transplanted organs and constitutively express Fas (CD95) ligand (FasL) on their surface. We investigated the role of porcine FasL in the generation of the human anti-pig response in vitro. Porcine aortic endothelial cells (PAEC) lysed a Fas+ human T-cell line, Jurkat. Anti-human Fas monoclonal antibody (mAb) specifically inhibited this killing in a dose-dependent manner, suggesting that porcine FasL recognizes and binds human Fas to induce apoptosis of human Fas+ cells. We next cloned porcine FasL, identifying an open reading frame of 849 base pairs predicting a protein of 282 amino acids. The predicted amino acid sequence was 85, 76, and 75% homologous to the predicted amino acid sequences of human, mouse, and rat, respectively, and found that PAEC expressed both FasL mRNA and protein. Transient transfection was used to increase or induce porcine FasL expression in PAEC or COS-7 cells. Transfection of PAEC with a plasmid encoding porcine FasL increased their ability to induce apoptosis in Jurkat cells, fresh human T cells activated with IL-2 and anti-CD3, and fresh IL-2-activated human (natural killer) NK cells. Moreover, porcine Fas L-transfected COS-7 cells induced significant apoptosis in Jurkat cells compared with that induced by mock-transfected COS-7 cells. Finally, the overexpression of porcine FasL in PAEC reduced their susceptibility as target cells to lysis by activated human NK or T cells. These findings suggest that porcine FasL overexpression in EC of vascularized xenografts may provide protection from cellular xenograft rejection.

Crucial Fas-Fas ligand interaction in spontaneous acceptance of hepatic allografts in mice

The Fas/Fas ligand (FasL) system plays important roles in the immune system, including host immunoregulation and cytotoxicity. In this study, we investigated the involvement of Fas-FasL interactions in spontaneous acceptance of hepatic allografts in murine orthotopic liver transplantation. Liver transplantation between the C57BL/6 (B6, H-2b) donor and the MRL/Mp (MRL, H-2k) recipient was performed in various combinations of donor and recipient mice with wild type (+/+), Fas-mutant (lpr) or FasL-mutant (gld) genotypes. The prolongation and spontaneous acceptance of the fully allogeneic grafts in recipients was not observed in either MRL-lpr recipients with B6+/+ livers or MRL+/+ recipients with B6-gld livers. Moreover, the serum alanine aminotransferase (ALT) levels and the degree of cell infiltration into hepatic allografts on day 7 after transplantation were inversely correlated with the recipient survival time (in days). The donor-specific cytotoxic T-lymphocyte (CTL) activities of the graft-infiltrating cells (GICs) from MRL-gld recipients with B6+/+ livers were much lower than those from MRL+/+ or -lpr recipients on days 5 and 10 after transplantation. However, the CTL activities of the GICs from MRL+/+ and -gld recipients predominantly disappeared by day 15 after transplantation. Furthermore, the anti-donor CTL activities induced in MRL+/+ recipients were ascribed to CD8+ cells, and were not mediated by Fas-FasL interactions. These results strongly suggest that the Fas/FasL system plays a critical role for recipient immunoregulation, enabling recipients in accepting hepatic allografts by deletion of the donor-specific T cells, but not for CTL/target cell interaction in MRL+/+ recipients.

Transfection of tubule cells with Fas ligand causes leukocyte apoptosis

BACKGROUND

Since the Fas/Fas Ligand (FasL) interaction is recognized as a major pathway of apoptosis in immune cells, we hypothesized that selective expression of FasL by tubular cells (TC) may promote the resolution of interstitial inflammation by inducing apoptosis of infiltrating immune cells. In this study, the effect of FasL transfection of rat TC on apoptosis of leukocytes was examined.

METHODS

Rat tubule cells (NRK52E) were transfected with plasmids constructed using human and rat FasL (hFasL and rFasL). The propensity of activated, transfected TC to undergo apoptosis was examined. Similarly, the effects of FasL transfection on apoptosis of Jurkat cells and activated leukocytes were assessed directly following co-culture for 12 hours and in a cell insert system intended to assess the effects of soluble FasL. Fas and FasL expression was assessed by flow cytometry and apoptosis was examined using Annexin V staining and the TUNEL method.

RESULTS

Expression of FasL in TC was increased after FasL transfection. Transfected TC showed no detectable increase in apoptosis following lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-alpha) activation. Jurkat cell apoptosis was increased ninefold and eightfold after co-culture with TC transfected with hFasL and rFasL, respectively (67.0 +/- 12.1% and 60.1 +/- 8.8% vs. 6.7 +/- 1.8% with un-transfected TC, P < 0.01). Similarly, apoptosis of activated leukocytes was increased fourfold by co-culture (26.8 +/- 4.9% vs. 6.7 +/- 2.0% with untransfected TC, P < 0.01). Leukocyte apoptosis also was increased in an insert culture system (18.2 +/- 4.4% vs. 5.8 +/- 2.3% with un- transfected TC, P < 0.01). No increase of TC apoptosis was detected in any of the co-culture experiments.

CONCLUSION

Enhanced expression of FasL by TC is capable of inducing apoptosis of activated leukocytes, without evidence for increased susceptibility to apoptosis of the transfected cells themselves. This suggests a potential role for this approach in the limitation and resolution of renal tubulointerstitial inflammation.

Cell death and immune privilege

The host response to pathogens involves complex inflammatory responses and immune reactions. While these are central to host defense and vital to clearing infections, they are often accompanied by injury to surrounding tissue. Most organ systems can tolerate these responses without permanent consequences. However, there are sites that limit the spread of inflammation because it can threaten organ function. The most prominent examples of these are the eye, brain, and reproductive organs (testis, ovary), where even minor bouts of inflammation can have long-term consequences for the survival of the organism. In these organs immune responses either do not proceed, or proceed in a manner different from other areas; thus, they are called "immunologically privileged." Here a functioning immune response can be the culprit that leads to disease.

Role of Fas ligand in ocular tissue

The expression of Fas ligand (FasL) in the eye is an important factor in the maintenance of immune privilege. Although FasL expression in donor corneas contributes to prolonged survival of orthotopic corneal allografts in solid organ transplantation, FasL gene-transfected tissues reportedly lead to graft destruction through neutrophil recruitment. Differences in the effects of FasL have been attributed to different roles of soluble FasL (sFasL) and membrane FasL (mFasL). This is based on the presumption that the signals through sFasL and mFasL differ, with one causing apoptosis and the other activating inflammation. It was recently reported that inflammation caused by FasL was inhibited at an immune-privileged site, and therefore the effects of FasL may depend on differences in the anatomic sites where FasL-expressing cells are located. In this article, we discuss the role of sFasL and mFasL in ocular immune privilege.

Preimplantation-stage stem cells induce long-term allogeneic graft acceptance without supplementary host conditioning

Hematopoietic stem cells have been successfully employed for tolerance induction in a variety of rodent and large animal studies. However, clinical transplantation of fully allogeneic bone marrow or blood-borne stem cells is still associated with major obstacles, such as graft-versus-host disease or cytoreductive conditioning-related toxicity. Here we show that when rat embryonic stem cell-like cells of WKY origin are injected intraportally into fully MHC-mismatched DA rats, they engraft permanently (>150 days) without supplementary host conditioning. This deviation of a potentially alloreactive immune response sets the basis for long-term graft acceptance of second-set transplanted WKY cardiac allografts. Graft survival was strictly correlated with a state of mixed chimerism, which required functional thymic host competence. Our results provide a rationale for using preimplantation-stage stem cells as vehicles in gene therapy and for the induction of long-term graft acceptance.

Gene therapy and solid-organ transplantation

Recent developments in transplantation medicine improved the short- and long-term survival of solid-organ transplantation. However, chronic allograft rejection, the side effects of the long-term immunosuppressive treatment, and organ shortage are still the major obstacles to achieving long-term survival. Gene therapy has the potential to meet these challenges and has unique advantages in transplantation. In this review we summarize the studies using gene therapy in solid-organ transplantation.

Exposure to exogenous DNA can modify the sensitivity of the Fas apoptotic pathway

BACKGROUND

Gene-transfer techniques are commonly employed for both in vitro and in vivo studies. However, modifications of the target cell following the introduction of the gene of interest are not often examined. These modifications can alter the immunogenicity and/or the susceptibility of the target cell to apoptosis and may produce unwanted consequences in vivo.

METHODS

Gene transfer into the murine fibroblastic Psi-CRIP packaging cell line was performed using calcium phosphate precipitation, cationic liposome-DNA complexes or a retroviral RNA-mediated method. After gene transfer, Fas expression, cytokine production, and sensitivity to Fas ligand (FasL)-mediated death were assessed.

RESULTS

Following transfection of a FasL expression vector by calcium phosphate precipitation, an unexpected increase was observed in apoptotic cell death in previously Fas-resistant Psi-CRIP cells. This apoptosis was due to Fas upregulation and an increase of sensitivity to FasL-mediated death. Other plasmids coding non-cytotoxic factors also modulated this apoptotic pathway. The co-stimulatory molecule CD80 was also upregulated. Exposure to naked DNA alone elicited the same response. The effect was not dependent on the methylation status of exogenous DNA, but was found to be dependent on the target cell type and might be avoided by the use of an RNA-mediated retroviral system.

CONCLUSIONS

Plasmid transfection or simple exposure to naked DNA can increase sensitivity to apoptosis. The generation of FasL packaging cell lines is therefore limited by an increase in FasL/Fas-mediated apoptosis. These findings should be considered when using genetically modified transplantable cells in order to prevent elimination by host cytotoxic cells and in particular when cells are engineered using FasL.

Death receptor ligands in tumors

Activation of apoptosis via death receptors is a tightly regulated event, and the death pathway itself is open to interference on the part of soluble or membrane-bound decoy receptors. The aggregation state of the death-inducing ligand is a crucial factor, particularly when these molecules are used as recombinant drugs against tumors. Whether tumors are sensitive to such ligands is determined by both the net abundance of death receptors versus decoy receptors and the balance between intracellular apoptotic and antiapoptotic mechanisms. This means that in vivo elimination of tumor cells by effector arms such as T lymphocytes, natural killer cells, macrophages, and dendritic cells is dependent on both the function of activated lymphoid cells and the genetic properties of tumor cells. Death receptor ligands, however, may be a double-edged sword. When expressed on cytotoxic T lymphocytes, natural killer cells, monocytes, and dendritic cells, they induce the apoptosis of many tumor cells, whereas their expression on tumor cells induces the apoptosis of killer cells. The in vivo result is influenced by the number of infiltrating cells, their state of activation, the cytokine repertoire in the tumor microenvironment, and the ability of the tumor to produce soluble factors inhibiting their cytolytic functions.

The role of Fas ligand in immune privilege

Immune privilege is a property of some sites in the body, whereby immune responses are limited or prevented. One explanation that has been proposed for this phenomenon is engagement of the pro-apoptotic molecule Fas by its ligand (FasL), which leads to apoptosis, and consequently limits an inflammatory response. This idea has recently been challenged, and here we review the evidence for and against a role for FasL in immune privilege.

Apoptosis and its clinical impact

BACKGROUND

Apoptosis or programmed cell death is an orderly cascade that can be regulated and ultimately results in the demise of the cell. Induction of apoptosis can occur by various chemical and biologic agents. Initiation of apoptosis leads to activation of effector molecules particularly caspases. These proteases cleave distinct protein substrates, resulting in the morphologic changes seen in apoptosis. This form of cell death is involved in almost every physiologic and pathogenic process in the body. For this reason the ability to control apoptosis has important therapeutic ramifications.

RESULTS

This article reviews the history of the investigation of apoptosis and summarizes the most important pathways and regulatory molecules involved in this process. The major regulators of apoptosis, including the Bcl-2, caspase, and inhibitor of apoptosis families, are examined. The two major apoptotic pathways, including the extrinsic/cell surface death receptor and the intrinsic/mitochondrial pathways, are discussed. A major emphasis is given to examining the relationship between apoptosis and certain disease processes. This review specifically focuses on the importance of apoptosis research in the development of new methods of management of cancer with an emphasis in head and neck oncology.

CONCLUSIONS

Apoptosis is a rapidly growing field. The understanding of the mechanisms and effector molecules controlling this form of cell death is evolving. On the basis of increasing knowledge of how programmed cell death is regulated and the improvements in designing and developing gene therapies and chemicals that are more accurate in targeting specific molecules, the control of apoptosis will become more important in the clinical setting. This possibility will open the door for new therapeutic endeavors in many areas of medicine and specifically in the area of oncology.

Immune privilege or inflammation? Insights into the Fas ligand enigma

Fas ligand (FasL) has become an enigmatic molecule: some evidence indicates that it contributes to immune privilege in tissues and tumors, whereas other data demonstrates that FasL can elicit inflammation. New findings may begin to reconcile the paradoxical effects of FasL.

Fulminant hepatitis by Fas-ligand expression in MRL-lpr/lpr mice grafted with Fas-positive livers and wild-type mice with Fas-mutant livers

BACKGROUND

Fulminant hepatitis in mice could be induced by gene-transfection of Fas ligand (FasL). However, the mechanisms of this event still remain controversial as to whether it is mediated by direct Fas/FasL interaction and/or neutrophil migration. To investigate the role of exogenous FasL-expression, we established a simple but clear mouse model on which we performed liver transplantation between Fas-mutant mice (MRL-lpr/lpr) and wild-type mice (MRL+/+).

METHODS

The controls were nontransplanted wild-type (group 1) and MRL-lpr/lpr (group 2) mice. We obtained recipients with a Fas defect only in the liver (group 3; MRL-lpr/lpr liver graft in wild-type mice) and Fas-defected recipients with Fas-positive livers (group 4; wild-type graft in MRL-lpr/lpr). We successfully expressed FasL in the liver by cotransfection of two types of adenoviral vectors, AxCALNFasL and AxCANCre, with a Cre-loxP switching system.

RESULTS

FasL-expression in the livers in groups 3 and 4 resulted in animal death due to fulminant hepatitis within 48 hr after administration of the vectors. We obtained similar findings in group 1, whereas the mice in group 2 survived without any evidence of hepatitis. Immune staining revealed a marked infiltration of CD11b-positive cells in group 1 and group 3. Despite the number of apoptotic cells, a few infiltration of CD11b-positive cells were seen in group 4. We observed no remarkable findings in the FasL-expressed livers in group 2.

CONCLUSION

The results indicated that exogenous FasL-expression induces hepatocyte apoptosis both by direct interaction with Fas and by recruiting Fas-positive inflammatory cells. These findings are important for generating a new strategy to prevent hepatitis as well as for understanding the role of the Fas/FasL interaction in the pathophysiology of hepatitis.

Induction of lymphocyte apoptosis in rat liver allograft with ongoing rejection by FTY720

The action mechanism of FTY720, a novel immunosuppressant, is completely different from conventional immunosuppressants. The drug, which triggers apoptosis in murine and human lymphocytes, has a potent immunosuppressive activity to prevent allograft rejection without any severe side-effect. The present study was designed to determine whether FTY720 induces apoptotic cell death in activated lymphocytes infiltrated into liver grafts with ongoing rejection. FTY720 was orally administered at 5 mg/kg to the recipients on day 3 and day 4 after grafting, when the graft rejection was histologically confirmed. The intragraft patterns of IL-2, interferon-gamma (IFN-gamma), perforin, and granzyme B gene expression were detected by reverse transcriptase-polymerase chain reaction. The treatment reversed ongoing rejection and significantly prolonged recipient survival time compared with the control group. Light microscopic observation of the graft sections stained with the DNA nick-end labelling method showed that the apoptosis in the control allografts was mainly induced in hepatocytes, while that in the FTY720-treated allografts was in infiltrated lymphocytes. The rejection therapy with FTY720 did not alter the expression of IL-2, IFN-gamma, and perforin mRNAs, but slightly decreased granzyme B expression. Our results suggest that FTY720 does not alter the intrinsic lymphocyte function to produce the rejection-related cytokines, but strongly induces apoptotic cell death in the activated lymphocytes. Thus, FTY720 affords new insight into the mechanisms underlying improvements in immunosuppressive treatments.

Analysis of alloreactivity and intragraft cytokine profiles in living donor liver transplant recipients with graft acceptance

Although some previous studies have indicated the possibility of immunosuppression withdrawal in clinical liver transplantation, the mechanism of graft acceptance is not clear. The aim of this study is to elucidate the alloreactivity against the donor and intragraft cytokine profiles in living donor liver transplant (LDLT) recipients with graft acceptance. In October 1999, we had 23 patients who survived without immunosuppression after LDLT with a median drug-free period of 25 months (range: 3-69 months). They consisted of six patients who were electively weaned by an elective weaning protocol and 17 either forcibly or accidentally weaned patients due to various causes but mainly due to infection. We evaluated the alloreactivity against the donor in these patients by a mixed lymphocyte reaction and intragraft cytokine profiles by real-time reverse transcriptase-polymerase chain reaction. The development of donor-specific hyporeactivity was observed in the patients with graft acceptance. The cytokine pattern in the supernatant of the culture medium revealed a down regulation of T helper (Th) 1 cytokine INF gamma against the donor while no significant difference was seen in Th2 cytokine IL-10. Regarding the intragraft cytokine profiles, we could find no amplification of Thl cytokines (IL-2, INF y) and IL-4 while some of the patients revealed a gene expression of IL-10 with no significant difference from that of the normal, untransplanted liver specimen. In addition, no difference was observed in any other cytokines (IL-1beta, IL-8, IL-15, TNFalpha) compared with those of the normal controls. We propose that the down regulation of Th1 cytokine is one possible mechanism of graft acceptance in LDLT recipients.

Gene therapy and transplantation

Advances in molecular biology and in techniques of gene transfer have resulted in the development of practical approaches to human gene therapy. Many applications are of relevance to manipulation of the immune system and have potential in organ and cell transplantation. For example, gene therapy approaches may facilitate the induction of immunological tolerance to a donor organ or protect it locally against the host's immune response. Based on a comprehensive review of the world literature, examples of current research efforts in both allogeneic and xenogeneic transplantation are presented and discussed.

Proinflammatory consequences of transgenic fas ligand expression in the heart

Expression of Fas ligand (FasL) renders certain tissues immune privileged, but its expression in other tissues can result in severe neutrophil infiltration and tissue destruction. The consequences of enforced FasL expression in striated muscle is particularly controversial. To create a stable reproducible pattern of cardiomyocyte-specific FasL expression, transgenic (Tg) mice were generated that express murine FasL specifically in the heart, where it is not normally expressed. Tg animals are healthy and indistinguishable from nontransgenic littermates. FasL expression in the heart does result in mild leukocyte infiltration, but despite coexpression of Fas and FasL in Tg hearts, neither myocardial tissue apoptosis nor necrosis accompanies the leukocyte infiltration. Instead of tissue destruction, FasL Tg hearts develop mild interstitial fibrosis, functional changes, and cardiac hypertrophy, with corresponding molecular changes in gene expression. Induced expression of the cytokines TNF-alpha, IL-1beta, IL-6, and TGF-beta accompanies these proinflammatory changes. The histologic, functional, and molecular proinflammatory consequences of cardiac FasL expression are transgene-dose dependent. Thus, coexpression of Fas and FasL in the heart results in leukocyte infiltration and hypertrophy, but without the severe tissue destruction observed in other examples of FasL-directed proinflammation. The data suggest that the FasL expression level and other tissue-specific microenvironmental factors can modulate the proinflammatory consequences of FasL.

Fas ligand gene transfer prolongs rat renal allograft survival and down-regulates anti-apoptotic Bag-1 in parallel with enhanced Th2-type cytokine expression

BACKGROUND

Fas ligand (FasL) induces apoptosis of cells bearing Fas receptor, and may play a role in the acquisition of immune privilege. We have previously shown that adenovirus (Ad)-mediated FasL gene transfer significantly prolongs survival in a strongly major histocompatibility complex-incompatible rat kidney allograft model. This study analyzes putative mechanisms of FasL-mediated effects, with particular emphasis on Th1 and Th2 immune activation and Bag-1 expression, a Bcl-2-binding anti-apoptotic protein.

METHODS

Kidney transplants were performed in Wistar-Furth to Lewis rat combination. Donor kidneys were perfused in situ with Ad-FasL or Ad-beta-Gal, and then transplanted. Kidney allografts were harvested at days 2, 7, and 56 and were evaluated by hematoxylin and eosin and immunohistochemical staining. The expression of FasL, Bag-1, and Th1/Th2 cytokine genes was assessed by Northern blots, Western blots, and competitive template reverse-transcriptase polymerase chain reaction, respectively.

RESULTS

Intragraft expression of FasL was enhanced, whereas that of anti-apoptotic Bag-1 gene was diminished throughout, in Ad-FasL-transduced well-functioning renal allografts, compared with Ad-beta-Gal-treated rejecting controls. In parallel, the expression of mRNA coding for IL-2 and IFN-gamma remained depressed, whereas that of IL-4 and IL-10 reciprocally and progressively increased in the Ad-FasL animal group.

CONCLUSIONS

Prolonged survival in Ad-FasL-transduced rat renal allograft model correlates with down-regulation of Bag-1, a novel anti-apoptotic gene, and preferential Th2-type cytokine elaboration profile at the graft site. Because Th1-like cells are sensitive to FasL-mediated cytotoxic effects, T-cell apoptosis may preferentially spare Th2-like cells, with resultant prolonged graft survival.

Tolerance of rat liver allografts induced by short-term selective immunosuppression combining monoclonal antibodies directed against CD25 and CD54 with subtherapeutic cyclosporine

BACKGROUND

Our purpose was to develop and evaluate protocols for selective immunosuppression after liver transplantation using the monoclonal antibodies (mAbs) NDS-61, directed against the interleukin-2 receptor (CD25), and 1A29, directed against the intercellular adhesion molecule-1 (CD54), in combination with subtherapeutic cyclosporine (CsA).

METHODS

Orthotopic rat liver transplantation (ORLT) was performed in a DA-to-LEW strain combination. Immunosuppression was administered from day 0 to +13. Functional parameters such as survival time, body weight, and serum bilirubin levels were measured and the liver grafts were evaluated histologically.

RESULTS

A stepwise tapering of CsA from 3 to 0.25 mg/kg/day reduced the long-term survival rate. All animals died at a CsA dosage of 0.25 mg/kg/day, which was therefore defined as subtherapeutic. Monotherapy with the anti-CD25 mAb was performed at dosages of 600 and 1800 microg/kg/day. The lower mAb dosage resulted in a long-term survival rate of 12% and was defined as subtherapeutic. The combination therapy of CsA (0.25 mg/kg/day) and anti-CD25 mAb (600 microg/kg/day) produced a synergistic effect and led to a long-term survival rate of 84%. This survival rate was significantly higher than those after either CsA (P<0.005) or anti-CD25 mAb (P<0.001) monotherapy. Both dosages (10 and 30 microg/kg/day) of anti-CD54 mAb monotherapy as well as anti-CD54 mAb combined with a subtherapeutic dosage of CsA were ineffective in preventing acute allograft rejection. The addition of anti-CD54 mAb (30 microg/kg/day) to combined CsA plus anti-CD25 mAb therapy (triple therapy), however, increased the long-term survival rate to 100%. In the triple therapy group there was no rejection process in the liver allografts at any time, and donor-specific tolerance could be shown by donor-specific and third-party heterotopic heart transplantation.

CONCLUSIONS

The synergistic action of subtherapeutic CsA plus anti-CD25 mAb NDS-60 could be demonstrated, whereas anti-CD54 mAb only had a positive effect in a triple therapy group. Triple therapy prevented both acute and chronic rejection and induced donor-specific tolerance.

Fas and Fas ligand in gut and liver

Apoptosis (programmed cell death) has been shown to play a major role in development and in the pathogenesis of numerous diseases. A principal mechanism of apoptosis is molecular interaction between surface molecules known as the "death receptors" and their ligands. Perhaps the best-studied death receptor and ligand system is the Fas/Fas ligand (FasL) system, in which FasL, a member of the tumor necrosis factor (TNF) family of death-inducing ligands, signals death through the death receptor Fas, thereby resulting in the apoptotic death of the cell. Numerous cells in the liver and gastrointestinal tract have been shown to express Fas/FasL, and there is a growing body of evidence that the Fas/FasL system plays a major role in the pathogenesis of many liver and gastrointestinal diseases, such as inflammatory bowel disease, graft vs. host disease, and hepatitis. Here we review the Fas/FasL system and the evidence that it is involved in the pathogenesis of liver and gastrointestinal diseases.