Kinetics of intragraft cytokine expression, cellular infiltration, and cell death in rejection of renal allografts compared with acceptance of liver allografts in a rat model: early activation and apoptosis is associated with liver graft acceptance

Transplant Tolerance, Not Only Clonal Deletion

The quest to understand how allogeneic transplanted tissue is not rejected and how tolerance is induced led to fundamental concepts in immunology. First, we review the research that led to the Clonal Deletion theory in the late 1950s that has since dominated the field of immunology and transplantation. At that time many basic mechanisms of immune response were unknown, including the role of lymphocytes and T cells in rejection. These original observations are reassessed by considering T regulatory cells that are produced by thymus of neonates to prevent autoimmunity. Second, we review "operational tolerance" induced in adult rodents and larger animals such as pigs. This can occur spontaneously especially with liver allografts, but also can develop after short courses of a variety of rejection inhibiting therapies. Over time these animals develop alloantigen specific tolerance to the graft but retain the capacity to reject third-party grafts. These animals have a "split tolerance" as peripheral lymphocytes from these animals respond to donor alloantigen in graft versus host assays and in mixed lymphocyte cultures, indicating there is no clonal deletion. Investigation of this phenomenon excludes many mechanisms, including anti-donor antibody blocking rejection as well as anti-idiotypic responses mediated by antibody or T cells. This split tolerance is transferred to a second immune-depleted host by T cells that retain the capacity to effect rejection of third-party grafts by the same host. Third, we review research on alloantigen specific inhibitory T cells that led to the first identification of the CD4+CD25+T regulatory cell. The key role of T cell derived cytokines, other than IL-2, in promoting survival and expansion of antigen specific T regulatory cells that mediate transplant tolerance is reviewed. The precise methods for inducing and diagnosing operational tolerance remain to be defined, but antigen specific T regulatory cells are key mediators.

Donor plasmacytoid dendritic cells modulate effector and regulatory T cell responses in mouse spontaneous liver transplant tolerance

We assessed the role of donor liver non-conventional plasmacytoid dendritic cells (pDCs) in spontaneous liver transplant tolerance in a fully MHC-mismatched (C57BL/6 (H2^b ) to C3H (H2^k )) mouse model. Compared with spleen pDCs, liver pDCs expressed higher levels of DNAX-activating protein of 12 kDa and its co-receptor, triggering receptor expressed by myeloid cells 2, and higher ratios of programed death ligand-1 (PD-L1):costimulatory CD80/CD86 in the steady state and after Toll-like receptor 9 ligation. Moreover, liver pDCs potently suppressed allogeneic CD4⁺ and CD8⁺ T cell proliferative responses. Survival of pDC-depleted livers was much poorer (median survival time: 25 days) than that of either untreated donor livers or pDC-depleted syngeneic donor livers that survived indefinitely. Numbers of forkhead box p3 (FoxP3)⁺ regulatory T cells in grafts and mesenteric lymph nodes of mice given pDC-depleted allogeneic livers were reduced significantly compared with those in recipients of untreated livers. Graft-infiltrating CD8⁺ T cells with an exhausted phenotype (programed cell death protein 1⁺ , T cell immunoglobulin and mucin domain-containing protein 3⁺ ) were also reduced in recipients of pDC-depleted livers. PD1-PD-L1 pathway blockade reversed the reduction in exhausted T cells. These novel observations link immunoregulatory functions of liver interstitial pDCs, alloreactive T cell exhaustion, and spontaneous liver transplant tolerance.

Understanding, predicting and achieving liver transplant tolerance: from bench to bedside

In the past 40 years, liver transplantation has evolved from a high-risk procedure to one that offers high success rates for reversal of liver dysfunction and excellent patient and graft survival. The liver is the most tolerogenic of transplanted organs; indeed, immunosuppressive therapy can be completely withdrawn without rejection of the graft in carefully selected, stable long-term liver recipients. However, in other recipients, chronic allograft injury, late graft failure and the adverse effects of anti-rejection therapy remain important obstacles to improved success. The liver has a unique composition of parenchymal and immune cells that regulate innate and adaptive immunity and that can promote antigen-specific tolerance. Although the mechanisms underlying liver transplant tolerance are not well understood, important insights have been gained into how the local microenvironment, hepatic immune cells and specific molecular pathways can promote donor-specific tolerance. These insights provide a basis for the identification of potential clinical biomarkers that might correlate with tolerance or rejection and for the development of novel therapeutic targets. Innovative approaches aimed at promoting immunosuppressive drug minimization or withdrawal include the adoptive transfer of donor-derived or recipient-derived regulatory immune cells to promote liver transplant tolerance. In this Review, we summarize and discuss these developments and their implications for liver transplantation.

Induction Phase of Spontaneous Liver Transplant Tolerance

The liver has long been known to possess tolerogenic properties. Early experiments in liver transplantation demonstrated that in animal models, hepatic allografts could be accepted across MHC-mismatch without the use of immunosuppression, and that transplantation of livers from the same donor was capable of inducing tolerance to other solid organs that would normally otherwise be rejected. Although this phenomenon is less pronounced in human liver transplantation, lower levels of immunosuppression are nevertheless required for graft acceptance than for other solid organs, and in a minority of individuals immunosuppression can be discontinued in the longer term. The mechanisms underlying this unique hepatic property have not yet been fully delineated, however it is clear that immunological events in the early period post-liver transplant are key to generation of hepatic allograft tolerance. Both the hepatic parenchyma and the large number of donor passenger leukocytes contained within the liver allograft have been demonstrated to contribute to the generation of donor-specific tolerance in the early post-transplant phase. In particular, the unique nature of hepatic-leukocyte interactions appears to play a crucial role in the ability of the liver to silence the recipient alloimmune response. In this review, we will summarize the evidence regarding the potential mechanisms that mediate the critical early phase in the generation of hepatic allograft tolerance.

Transplant Tolerance Induction: Insights From the Liver

A comparison of pre-clinical transplant models and of solid organs transplanted in routine clinical practice demonstrates that the liver is most amenable to the development of immunological tolerance. This phenomenon arises in the absence of stringent conditioning regimens that accompany published tolerizing protocols for other organs, particularly the kidney. The unique immunologic properties of the liver have assisted our understanding of the alloimmune response and how it can be manipulated to improve graft function and survival. This review will address important findings following liver transplantation in both animals and humans, and how these have driven the understanding and development of therapeutic immunosuppressive options. We will discuss the liver's unique system of immune and non-immune cells that regulate immunity, yet maintain effective responses to pathogens, as well as mechanisms of liver transplant tolerance in pre-clinical models and humans, including current immunosuppressive drug withdrawal trials and biomarkers of tolerance. In addition, we will address innovative therapeutic strategies, including mesenchymal stem cell, regulatory T cell, and regulatory dendritic cell therapy to promote liver allograft tolerance or minimization of immunosuppression in the clinic.

Role of programmed death ligand 1 and Kupffer cell in immune regulation after orthotopic liver transplantation in rats

INTRODUCTION

Role of programmed death ligand 1 (PD-L1) and Kupffer cells (KCs) in liver transplantation immune regulation was unclear.

METHODS

Lewis and Brown-Norway (BN) rats were assigned to LEW-BN group (Lewis-to-BN liver transplantation) and BN-BN group (BN-to-BN). Receipts were sacrificed for histology and assessment of cytokines and PD-L1 production. Effect of PD-L1 and KCs on T cells (TCs) was monitored by co-culture of ³H-Thymidine TCs. KCs transfected with PD-L1-shRNA interference plasmids were co-cultured with TCs, PD-L1 expression and cytokines production were measured respectively.

RESULTS

Recipients in BN-BN group survived a long time while acute rejection was found in LEW-BN group. ELISA showed plasma levels of IL-2, IFN-γ and TNF-α in BN-BN group were significantly lower and levels of IL-10 were significantly higher than that in LEW-BN group on day 7 after transplantation (P<0.05). PD-L1 expression of KCs in BN-BN group was significantly higher than that in the LEW-BN group (P<0.05). Proliferation rate of TCs in KCs+TCs group was significantly lower and its apoptosis rate was significantly higher than that in TCs group (P<0.05). IL-2, TNF-α and INF-γ levels were remarkably higher and IL-10 levels were lower in KCs+TCs group than that in TCs group (P<0.05). Levels of IL-2, IFN-γ and TNF-α in transfection group were significantly higher and that of IL-10 was notably lower than that in the un-transfected group (P<0.05).

CONCLUSION

KCs with high expression of PD-L1 could significantly suppress the proliferation and function of TCs. Silencing the expression of PD-L1 in KCs in vivo could restore the function of TCs.

Avoiding immunological rejection in regenerative medicine

One of the major goals of regenerative medicine is repair or replacement of diseased and damaged tissues by transfer of differentiated stem cells or stem cell-derived tissues. The possibility that these tissues will be destroyed by immunological rejection remains a challenge that can only be overcome through a better understanding of the nature and expression of potentially immunogenic molecules associated with cell replacement therapy and the mechanisms and pathways resulting in their immunologic rejection. This review draws on clinical experience of organ and tissue transplantation, and on transplantation immunology research to consider practical approaches for avoiding and overcoming the possibility of rejection of stem cell-derived tissues.

Mechanisms of murine spontaneous liver transplant tolerance

Liver transplant is associated with the induction of peripheral immune tolerance. Liver allografts are accepted spontaneously in most combinations of mismatch in major histocompatibility complex, without any requirements for immunosuppression. Liver nonparenchymal cells (especially dendritic cells and Kupffer cells), costimulatory pathways, and activated T-cell apoptosis may contribute to the induction of liver tolerance. Therefore, liver tolerance is an active process that includes T-cell activation, proliferation, infiltration of the allograft, and T-cell apoptosis. Liver dendritic cells may modulate the amount of alloreactive T cells in liver graft recipients by expressing the coinhibitory molecule programmed death-ligand 1 and the immunosuppressive enzyme indoleamine 2,3-dioxygenase. Liver dendritic cells also may induce activated T-cell apoptosis and Foxp3+ regulatory T cells. Future studies may clarify the precise function of liver nonparenchymal cells, the interactions between programmed death-ligand 1 and other costimulatory signals, and the contribution of the liver microenvironment to the induction and expansion of Foxp 3 regulatory T cells.

Infiltrating Foxp3(+) regulatory T cells from spontaneously tolerant kidney allografts demonstrate donor-specific tolerance

Foxp3(+) regulatory T cells (Tregs) have an essential role in immune and allograft tolerance. However, in both kidney and liver transplantation in humans, FOXP3(+) Tregs have been associated with clinical rejection. Therefore, the role and function of graft infiltrating Tregs have been of great interest. In the studies outlined, we demonstrated that Foxp3(+) Tregs were expanded in tolerant kidney allografts and in draining lymph nodes in the DBA/2 (H-2(d) ) to C57BL/6 (H-2(b) ) mouse spontaneous kidney allograft tolerance model. Kidney allograft tolerance was abrogated after deletion of Foxp3(+) Tregs in DEpletion of REGulatory T cells (DEREG) mice. Kidney allograft infiltrating Foxp3(+) Tregs (K-Tregs) expressed elevated levels of TGF-β, IL-10, interferon gamma (IFN-γ), the transcriptional repressor B lymphocyte-induced maturation protein-1 (Blimp-1) and chemokine receptor 3 (Cxcr3). These K-Tregs had the capacity to transfer dominant tolerance and demonstrate donor alloantigen-specific tolerance to skin allografts. This study demonstrated the crucial role, potency and specificity of graft infiltrating Foxp3(+) Tregs in the maintenance of spontaneously induced kidney allograft tolerance.

Predicting operational tolerance in pediatric living-donor liver transplantation by absence of HLA antibodies

BACKGROUND

The role of anti-human leukocyte antigen (HLA) antibodies in operational tolerance (OT) after pediatric living-donor liver transplantation (LDLT) remains inconclusive. We investigated whether the presence of HLA antibodies impeded the development of OT.

METHODS

We retrospectively examined the prevalence of anti-HLA antibodies in pediatric LDLT recipients before transplantation and at 3 weeks after transplantation and analyzed the significance of those antibodies in relation to later OT. Forty pediatric LDLTs were performed between April 1996 and December 2000 and followed up through July 2011, with sera available for measurement of HLA antibodies. Seventeen patients achieved OT (mean follow-up, 4571.9±544.7 days) and 23 patients did not achieve OT (mean follow-up, 4532.0±425.4 days). Protocol liver biopsy was done for 14 OT patients and 16 non-OT patients. Their sera were tested for anti-HLA class I and II antibodies using the LABScreen single antigen beads test, in which a 1000 mean fluorescence value was considered positive.

RESULTS

The prevalence of antibodies after transplantation in non-OT patients was higher than in OT patients (95.2% vs. 73.3%; P<0.001). The highest mean fluorescence intensity of antibodies was significantly higher in non-OT patients than in OT patients. The prevalence of HLA-B, HLA-C, HLA-DQ, and HLA-DR antibodies was significantly higher in non-OT patients than in OT patients. The highest mean fluorescence intensity of HLA-A, HLA-B, and HLA-DQ observed in non-OT patients was significantly higher than those in OT patients.

CONCLUSIONS

In our study, posttransplantation HLA antibodies were associated with the future absence of OT. A prospective study with more patients is necessary to confirm the predictive value of HLA antibodies for OT.

Expression of common gamma chain signalling cytokines and their receptors distinguishes rejection from tolerance in a rat organ transplant model

BACKGROUND

Signalling through the cytokine common γ chain (γc) is crucial for survival of activated T cells. In its absence, severe combined immunodeficiency ensues and transplanted tissues are not rejected.

METHODS

To determine whether differences in the availability of γc signalling cytokines correlate with rejection or acceptance, we examined expression of all γc signalling components in organs transplanted between PVG donors and DA recipients. In this combination hearts or kidneys are rejected in <10 days while livers survive >100 days. Expression of the γc cytokines IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21 and their receptors γc, IL-2Rα, IL-2Rβ/IL-15Rβ, IL-4Rα, IL-7Rα, IL-9Rα, IL-15Rα and IL-21Rα was determined by real-time PCR pre-transplant and on days 3, 5 and 7 after transplantation.

RESULTS

Most increased after transplantation, although there were significantly lower levels of IL-2, IL-2Rα, IL-4 and IL-15Rα in tolerant livers compared to rejecting hearts or kidneys. IL-9 was only expressed in normal kidneys and decreased during rejection. IL-15 was constitutively expressed and did not change after transplantation. IL-21 and IL-21R increased in all transplanted organs to a similar extent. IL-7Rα in liver was considerably increased compared with heart or kidney, consistent with its known inverse relationship to global levels of γc signalling.

CONCLUSIONS

In transplanted livers, acceptance is associated with low levels of all γc cytokines or receptors except IL-21. This is consistent with "dilution" of γc cytokines from a finite clone size of alloreactive T cells in livers, which are ten times larger than kidneys or hearts.

Tolerance in liver transplantation

Operational tolerance (OT) in liver transplant patients occurs much more frequently than OT of other transplanted organs; however the rate of OT varies considerably with the centre and patient population. Rates of OT range from 15% of the total liver transplant (LTX) patient population down to less than 5%. This review examines the reports of liver OT and compares the factors that could contribute to this variation. Multiple factors were examined, including the time from transplantation when weaning of immunosuppression (IS) was commenced, the rapidity of weaning, the contribution of maintenance and induction IS and the patient population transplanted. The approaches that might be used to increase the likelihood of OT are discussed and the approaches to monitoring OT in LTX patients are reviewed.

Approaching the promise of operational tolerance in clinical transplantation

Long-term acceptance of transplanted organs without requirement for indefinite immunosuppression remains the ultimate goal of transplant clinicians and scientists. This clinical state of allograft acceptance termed "operational tolerance" has been elusive in routine practice. However, there are published reports of recipients where immunosuppression has been discontinued, by intention or patient noncompliance, in which the outcome is a nondestructive immune response and normal function. The question now arises how clinical operational tolerance might be achieved in the majority of recipients. This review provides an overview of current approaches to achieve operational tolerance, including the use of donor bone marrow and depletion of recipient T cells and the resistance of liver transplants to rejection. It also describes the key role of clinical immune monitoring and future approaches to tolerance induction including inhibition of T-cell signaling, manipulation of costimulatory pathways, and expansion of regulatory T cells. The principles of these experimental approaches may ultimately be extended to provide safe and effective control of transplant rejection and induction of clinical operational tolerance.

Spontaneous acceptance of mouse kidney allografts is associated with increased Foxp3 expression and differences in the B and T cell compartments

Spontaneous acceptance of organ allografts can identify novel mechanisms of drug-free transplantation tolerance. Spontaneous acceptance occurs in both mouse kidney transplants and rat liver transplants however the early immune processes of mouse kidney acceptance have not been studied. Acceptance of C57BL/6 strain kidney allografts in fully MHC-incompatible B10.BR recipients was compared with rejection (REJ) of heart allografts in the same strain combination. Graft infiltrate and antibody deposition were examined by immunohistochemical staining. Expression of mRNA was measured by quantitative real-time PCR. Apoptosis was examined by TUNEL staining. The majority of kidney allografts were accepted long-term and induced tolerance (TOL) of donor-strain skin grafts, showing that acceptance was not due to immune ignorance. There was an extensive infiltrate of T cells in the TOL kidney that exceeded the level in REJ hearts but subsequently declined. The main differences were deposition of IgG2a antibody in REJ that was absent in TOL, more B cells infiltrating TOL kidneys and a progressive increase in the ratio of CD8:CD4 cells during rejection. There was also significantly greater Foxp3 mRNA expression in TOL. Kidneys from RAG-/- donors were accepted, showing that donor lymphocytes were not necessary for acceptance. Neutralising antibodies to TGF-β administered from day 0 to day 6 did not prevent TOL. On the basis of cytokine expression and apoptosis there was no evidence for immune deviation or deletion as mechanisms of acceptance. In accord with the findings of spontaneous acceptance of liver allografts in rats, the main difference between mouse kidney TOL and heart REJ was in the B cell compartment. The major difference to rat liver allograft acceptance was that apoptosis of infiltrate did not appear to play a role. Instead, increased Foxp3 expression in TOL kidneys implies that regulatory T cells might be important.

Liver grafts contain a unique subset of natural killer cells that are transferred into the recipient after liver transplantation

In contrast to other solid organ transplantations, liver grafts have tolerogenic properties. Animal models indicate that donor leukocytes transferred into the recipient after liver transplantation (LTX) play a relevant role in this tolerogenic phenomenon. However, the specific donor cell types involved in modulation of the recipient alloresponse are not yet defined. We hypothesized that this unique property of liver grafts may be related to their high content of organ-specific natural killer (NK) and CD56(+) T cells. Here, we show that a high proportion of hepatic NK cells that detach from human liver grafts during pretransplant perfusion belong to the CD56bright subset, and are in an activated state (CD69(+)). Liver NK cells contained perforin and granzymes, exerted stronger cytotoxicity against K562 target cells when compared with blood NK cells, and secreted interferon-gamma, but no interleukin-10 or T helper 2 cytokines, upon stimulation with monokines. Interestingly, whereas the CD56bright subset is classically considered as noncytolytic, liver CD56bright NK cells showed a high content of cytolytic molecules and degranulated in response to K562 cells. After LTX, but not after renal transplantation, significant numbers of donor CD56dim NK and CD56(+) T cells were detected in the recipient circulation for approximately 2 weeks. In conclusion, during clinical LTX, activated and highly cytotoxic NK cells of donor origin are transferred into the recipient, and a subset of them mixes with the recirculating recipient NK cell pool. The unique properties of the transferred hepatic NK cells may enable them to play a role in regulating the immunological response of the recipient against the graft and therefore contribute to liver tolerogenicity.

PD-1/B7-H1 interaction contribute to the spontaneous acceptance of mouse liver allograft

The programmed death-1 (PD-1)/B7-H1 pathway acts as an important negative regulator of immune responses. We herein investigated the role of the PD-1/B7-H1 pathway in establishing an immunological spontaneous tolerance status in mouse liver allografting. B7-H1 is highly expressed on the donor-derived tissue cells and it is also associated with the apoptosis of infiltrating T cells in the allografts. Strikingly, a blockade of the PD-1/B7-H1 pathway via anti-B7-H1mAb or using B7-H1 knockout mice as a donor led to severe cell infiltration as well as hemorrhaging and necrosis, thus resulting in mortality within 12 days. Furthermore, the expression of the FasL, perforin, granzyme B, iNOS and OPN mRNA in the liver allografts increased in the antibody-treated group in comparison to the controls. Taken together, these data revealed that the B7-H1 upregulation on the tissue cells of liver allografts thus plays an important role in the apoptosis of infiltrating cells, which might play a critical role of the induction of the spontaneous tolerance after hepatic transplantation in mice.

Statins induce immunosuppressive effect on heterotopic limb allografts in rat through inhibiting T cell activation and proliferation

Long-term use of immunosuppressive agents could bring many side effects. Recently, 3-Hydroxy-3-methyl-gutaryl coenzyme A reductase inhibitors (statins) have been reported to be immunomodulatory besides lowering serum cholesterol level. The aim of this study was to investigate the effects of statins on composite tissue allografts and T lymphocyte in vivo and in vitro. Rats were divided into 5 groups: syngeneic transplantation group (Lewis-Lewis); allogeneic control group (Brown Norway-Lewis, no treatment); low-dose statins group (15 mg /kg); high-dose statins group (30 mg /kg) and cyclosporin A group. In vivo, treatment of statins significantly prolonged allografts survival as compared to control group. Histological findings further supported these clinical results and demonstrated less extent of rejection. Immunohistochemical analysis showed that there was a remarkably reduced T cells infiltration in statins groups. Moreover, the serum levels of IL-2 and IFN-gamma were decreased after statins therapy, while these in control group increased significantly. Meanwhile, transcriptional activities of IL-2 and IFN-gamma were also dramatically down-regulated after statins treatment. In vitro, mixed lymphocyte reaction assay was performed and the results revealed lymphocyte proliferation was inhibited by statins in a dose-dependent manner. Furthermore, administration of statins exhibited inhibitory effects on CD3/CD28 mediated T cell activation and proliferation. Besides, the results demonstrated that statins significantly down-regulated mRNA expression and suppress cytokine production of IL-2 and IFN-gamma in vitro. In conclusion, our data demonstrated that application of statins could induce immunosuppressive effect and prolong allografts survival through inhibiting activation and proliferation of T cell and reducing production of IL-2 and IFN-gamma.

Blocking indoleamine dioxygenase activity early after rat liver transplantation prevents long-term survival but does not cause acute rejection

In a well-characterized rat model of liver transplantation, Piebald Virol Glaxo strain livers are accepted long term in fully mismatched Dark Agouti recipients (tolerance; TOL), but rejected in Lewis recipients (rejection; REJ). Spontaneous tolerance induction is associated with increased interferon-gamma expression, and we examined the role of the interferon-gamma-inducible immunomodulatory enzyme indoleamine dioxygenase (IDO) in this model. On day 3 after transplantation, IDO expression in the spleen of TOL recipients was significantly greater than in REJ. The B-cell population accounted for this early IDO increase. Intragraft expression of IDO increased to the same extent in both TOL and REJ. IDO inhibition for 7 days after transplantation reduced survival, but did not cause acute rejection of the liver in the TOL model. In conclusion, the differential IDO expression by B lymphocytes in the spleen of TOL recipients is not critical for preventing acute rejection.

Role of Kupffer cells in the induction of tolerance of orthotopic liver transplantation in rats

Because the role of Kupffer cells (KCs) in liver transplantation (LT) tolerance is not well understood, we investigated their role in liver allograft acceptance in rats. Male Sprague-Dawley rats were randomly assigned to either an LT group or a transplantation group pretreated with GdCl(3) (Gd group). The rats were postoperatively sacrificed at indicated times for histology and assessment of KC function, nuclear factor kappa B (NF-kappaB) activity, and cytokine production. KCs and T cells (TCs) were isolated from allografts to assess Fas/Fas ligand (FasL) expression. Cytotoxicity of KCs against TCs was monitored by coculturing of (3)H-thymidine TCs with KCs at various effector-to-target ratios. The results were as follows. First, grafts were spontaneously accepted in the LT group with evident apoptosis of TCs; however, inhibition of KCs by pretreatment with GdCl(3) decreased TC apoptosis and shortened the survival of allografts. Second, KCs in the LT group had increased levels of FasL messenger RNA and protein with respect to that in the Gd group. Third, by in vitro cocultivation assays, KCs induced TC apoptosis though elevated expression of FasL, and this process could be blocked by anti-FasL antibody. Fourth, there was a positive correlation between activation of NF-kappaB and FasL expression in KCs and interleukin-4 production in the LT group, and the activation of NF-kappaB was inhibited by pretreatment with GdCl(3). In conclusion, KC-induced depletion of TCs via the Fas/FasL pathway might play a critical role in LT tolerance. However, the tolerance is abrogated by suppression of FasL and IL-4 expression via inhibition of NF-kappaB activity by GdCl(3).

Monitoring tolerance after human liver transplantation

The validation of reliable, non-invasive immunological assays evaluating anti-donor responsiveness in allograft recipients would provide a clinically relevant tool for the early detection of ongoing rejection process as well as for the identification of operational tolerance in the long term. A sequential approach towards immunological monitoring of allografts is proposed in this review: (i) investigations exploring the initial donor-recipient alloresponses, including the analysis of the cytokine network; (ii) investigations regarding graft acceptance and operational tolerance in long-term transplant patients, consisting in the analysis of regulatory T cells and of circulating precursors of dendritic cells, in the measurement of T cell alloreactivity as well as in the study of T cell receptor repertoires. Beside the conventional in vivo and in vitro immunological techniques, the potential applications of molecular imaging in transplantation also deserve further exploration, with particular respect to allograft immune monitoring. Enforced collaboration between transplant clinicians and immunologists will be required to develop the translational research protocols required for the development of immunological monitoring, within an international multicentric network.

Gene array analysis of a rat model of liver transplant tolerance identifies increased complement C3 and the STAT-1/IRF-1 pathway during tolerance induction

This study aimed to define the molecular mechanism during induction of spontaneous liver transplant tolerance using microarrays and to focus on molecular pathways associated with tolerance by meta-analysis with published studies. The differences in the early immune response between PVG to DA liver transplant recipients that are spontaneously tolerant (TOL) and PVG to Lewis liver transplants that reject (REJ) were examined. Spleens from TOL and REJ on days 1 and 3 were compared by 2 color microarray. Forty-six of 199 genes differentially expressed between TOL and REJ had an immunological function. More immune genes were increased in TOL vs. REJ on day 1, including STAT-1, IRF-1 and complement C3. Differential expression of selected genes was confirmed by quantitative RT-PCR. The results were compared to two published high-throughput studies of rat liver transplant tolerance and showed that C3 was increased in all three models, while STAT-1 and IRF-1 were increased in two models. The early increases in immune genes in TOL confirmed previous reports of an active early immune response in TOL. In conclusion, the increase in STAT-1, IRF-1 and complement component C3 in several models of liver transplant tolerance suggests that the STAT-1/IRF-1 apoptotic pathway and C3 may be involved in the tolerogenic mechanism.

Posttransplant Interleukin-4 Treatment Converts Rat Liver Allograft Tolerance to Rejection

BACKGROUND

Previous studies showed that liver transplant rejection in the Piebald Virol Glaxo (PVG)-to-Lewis combination was associated with more intragraft interleukin (IL)-4 mRNA expression than in spontaneously tolerant grafts in the PVG-to-Dark Agouti (DA) combination. There was also immunoglobulin (Ig) G1 antibody deposition, suggesting an IL-4-induced IgG class switch in rejection. The aim of this study was to investigate whether IL-4 treatment converts PVG-->DA liver transplant tolerance to rejection.

METHODS

DA (RT1a) rats were recipients of orthotopic PVG (RT1c) liver transplants and DA liver transplants were syngeneic controls. Supernatant from IL-4-transfected Chinese hamster ovary cells (0.5 mL, 30,000 U) or from untransfected cells was injected intraperitoneally on days 3 through 7. Samples were taken for immunohistochemical staining of frozen tissue sections to analyze cellular infiltrate and antibody deposition.

RESULTS

IL-4 treatment significantly reduced survival of liver allografts from greater than 100 days in untreated animals to 9 days (P=0.004). Pathologic analysis of IL-4-treated animals showed that death was caused by liver transplant rejection, with a heavy infiltrate of mononuclear cells, disruption of portal tract areas, and infarction. Immunohistochemistry revealed an extensive infiltrate of T cells, CD25-expressing cells, and B cells that was similar to the level in PVG--> Lewis liver allograft recipients that reject the liver. There was also a more extensive monocyte-macrophage infiltrate and more major histocompatibility complex class II expression in IL-4-treated animals compared with untreated animals. There was moderate increase of IgM, little IgG1, and no IgE or IgG2a antibody deposition.

CONCLUSIONS

IL-4, a T-helper type 2 cytokine that has previously been shown to inhibit delayed-type hypersensitivity responses such as rejection, was found to promote rejection of liver allografts. There was only slight evidence of a graft-specific antibody response, showing that IL-4 induces liver allograft rejection in association with some, but not all, of the changes accompanying rejection in the PVG-->Lewis strain combination.

Apoptosis and the expression of genes of the Bcl-2 family and TGF-beta1 in rat renal allografts transplanted after donor-specific blood transfusion

Factors involved in "operational" tolerance in animal models induced by recipient pre-treatment with donor-specific blood transfusion (DSBT) need elucidation. This study examined apoptosis, expression of genes of the Bcl-2 family and of TGF-beta(1) in isografts, rejecting and tolerant allografts.

METHODS

Adult inbred Dark Agouti (DA) kidneys were transplanted, with immediate nephrectomy of recipient kidneys, to (1) ALLO, inbred Albino Surgery (AS) rats; (2) DSBT ALLO, AS rats who received two DA blood transfusions under cover of cyclosporine prior to transplantation; or (3) ISO, DA rats. Grafts were retrieved on day 1, 3, or 5. Apoptosis was assessed by TUNEL. RNA was extracted and reverse transcribed to cDNA for quantification by real-time PCR, relative to the 18s housekeeping gene.

RESULTS

Apoptosis was negligible in ISO while it increased in allograft groups from day 1. On day 5, apoptosis in ALLO (114.0 +/- 30.6), involved renal tubular cells and leukocytes compared to DSBT ALLO (9.7 +/- 4.0) and ISO (0.9 +/- 0.3) involving leukocytes only. On day 1, DSBT ALLO had higher expression of Bax than ALLO or ISO. On day 3, DSBT ALLO and ALLO had higher TGF-beta(1) mRNA than ISO. On day 5, Bcl-2 expression was significantly decreased (P < .001) in ALLO compared to DSBT ALLO and ISO. Bad and Bid were higher in DSBT ALLO than in ALLO. TGF-beta(1) was higher in DSBT ALLO compared to ISO.

CONCLUSIONS

Decreased expression of anti-apoptotic Bcl-2 gene may be implicated in increased apoptosis in rejecting allograft while expression of pro-apoptotic genes may be involved in the establishment of operational tolerance.

Adenovirus-mediated CTLA4Ig gene inhibits infiltration of immune cells and cell apoptosis in rats after liver transplantation

AIM: To investigate the role of adenovirus-mediated CTLA4Ig gene therapy in inhibiting the infiltration of macrophages and CD8+T cells and cell apoptosis after liver transplantation.

METHODS: The rat orthotopic liver transplantation model was applied. The rats were divided into three groups: group I: rejection control (SD-to-Wistar); group II: acute rejection treated with intramuscular injection of CsA 3.0 mg/(kg·d) for 12 d (SD-to-Wistar+CsA); groupIII: injection of 1×10⁹ PFU adenovirus-mediated CTLA4Ig gene liquor in dorsal vein of penis 7 d before liver transplantation (SD-to-Wistar+CTLA4Ig). Immunohistochemistry and transferase-mediated dUTP nick-end labeling (TUNEL) were used to analyze the expression of CTLA4Ig gene in liver, infiltration of macrophages and CD8+T cells, cell apoptosis in grafts at different time-points after liver transplantation. Histopathological examination was done.

RESULTS: CTLA4Ig gene expression was positive in liver on d 7 after administering adenovirus-mediated CTLA4Ig gene via vein, and remained positive until day 60 after liver transplantation. Infiltration of macrophages and CD8+T cells in CTLA4Ig-treated group was less than in rejection control group and CsA-treated group. The apoptotic index of rejection group on d 3, 5, and 7 were significantly higher than that of CTLA4Ig-treated group. A good correlation was found between severity of rejection reaction and infiltration of immune activator cells or cell apoptotic index in grafts.

CONCLUSION: CTLA4Ig gene is constantly expressed in liver and plays an important role in inducing immune tolerance.

Participation of RANTES and T-Cell Apoptosis in Human Renal Allograft

The aim of this study was to evaluate the serum RANTES (Regulated upon Activation of Normal T cell Expressed and Secreted) levels and the expression of CCR5, as well as the percentage of apoptotic cells, in peripheral T lymphocytes from renal transplanted patients with acute rejection (AR), chronic rejection (CR) or stable evolution (SE). RANTES serum levels were determined by enzyme-linked immunoadsorbent assay and CCR5 expression, as well as the percentage of apoptotic lymphocytes, on a FACScan flow cytometer. After staining with different antibodies, the cells were subjected to three-colour flow cytometric analysis. Data analysis was performed using winmdi 2.5 software. The serum RANTES level and percentages of CCR5/CD4 and CCR5/CD8 T lymphocytes in CR, AR and SE were lower than that in the control group (P <0.05). The level of CD4 and CD8 T lymphocytes in early apoptosis was higher in AR patients than in CR, SE or C groups (P <0.05). In the case of late apoptosis, the percentage of apoptotic/necrotic cells was higher in the CR than AR, SE or C groups (P <0.05). The RANTES serum levels and the percentage of peripheral CCR5 T lymphocytes would not indicate the renal allograft state. The increase of early apoptotic T lymphocytes could be a marker of AR process and could also indicate the initial step in reducing the cytotoxic T lymphocytes, thus favouring the graft evolution.

Combined donor leucocyte administration and immunosuppressive drug treatment for survival of rat heart allografts

BACKGROUND

Donor leucocytes (DL) play an important role in rat liver transplant tolerance and their postoperative administration can convert rejection to tolerance. They appear to induce early activation, altered patterns of infiltration and death of recipient alloreactive T cells. The ability of immunosuppressive drugs to combine with DL administration was examined in a rat heart transplant model.

METHODS

Immediately after PVG to DA heterotopic heart transplantation, 6 x 10(7) spleen DL were injected. Cyclosporine A (CsA), 1.5 mg/kg/day, or methotrexate (MTX), 0.1 or 0.2 mg/kg/day, were given from day (d) 0 to d4 (early) or from d3 to d7 (delayed). Castanospermine (CAST) was administered from d0 to d7 at 100 or 300 mg/kg/day. In a separate experiment, transplanted hearts and recipient spleens were collected from treatment groups for analysis of infiltrate and cytokine mRNA expression.

RESULTS

Delayed treatment with CsA or early treatment with MTX but not CAST combined with DL to result in prolonged graft survival. Recipients treated with DL and delayed CsA had a reduced level of intra-graft interleukin (IL)-2, interferon (IFN)-gamma, IL-4, and IL-4R mRNA expression and reduced infiltrate compared to DL alone. Early MTX plus DL led to almost complete inhibition of all markers of inflammation during treatment followed by a rapid increase after cessation. In combination with DL, CsA was more effective than MTX for induction of donor-specific tolerance at the dose and administration regimens tested.

CONCLUSIONS

Delayed CsA or early MTX combine with DL to prolong heart allograft survival. Early and extensive inhibition of rejection by MTX was less effective than delayed and partial inhibition of the response by CsA for induction of transplant tolerance.

Increased mononuclear cell activation and apoptosis early after human liver transplantation is associated with a reduced frequency of acute rejection

Experimental models of orthotopic liver transplantation (OLT) have shown that the very early events post-OLT are critical in distinguishing immunogenic and tolerogenic reactions. In rodents, increased leukocyte apoptosis and cytokine expression have been demonstrated in tolerogenic strain combinations. Information from human OLT recipients is less abundant. The aim of this study was to determine the amount of early leukocyte activation and apoptosis following human OLT, and to correlate this with subsequent rejection status. Peripheral blood mononuclear cells (PBMC) were isolated from 76 patients undergoing OLT - on the day prior, 5 hrs after reperfusion (day 0), and 18-24 hrs post-OLT (day 1). The mean level of apoptotic PBMCs on post OLT day 1 was higher than healthy recipients (0.9% +/- 0.2 vs. 0.2% +/- 0.1, p=0.013). Apoptosis was greater in nonrejecting (NR) (1.1% +/- 0.3) compared with acutely-rejecting (R) (0.3% +/- 0.1, p=0.021) patients. On day 1, PBMC from NR patients had increased expression of IFN-gamma (p=0.006), IL-10 (p=0.016), and CD40 ligand (p=0.02) compared with R. Donor cell chimerism on day 1 did not differ between the groups indicating that this was unlikely to account for increased PBMC apoptosis in the NR group. Interestingly, the level of chimerism on day 0 was significantly higher in NR (3.8% +/- 0.6) compared with R (1.2% +/- 0.4, p=0.004) patients and there was a close correlation between chimerism on day 0 and cytokine expression on day 1. These results imply that similar mechanisms are occurring in the human liver to promote graft acceptance as in the experimental models of liver transplantation and suggest that strategies that promote liver transplant acceptance in rodents might be applicable to humans.

A short course of mycophenolate immunosuppression inhibits rejection, but not tolerance, of rat liver allografts in association with inhibition of interleukin-4 and alloantibody responses

BACKGROUND

Some immunosuppressive drug therapies inhibit transplant tolerance in animal models, and we have shown that treatment of recipients with methylprednisolone, but not cyclosporine, inhibits spontaneous acceptance of liver transplants. This study investigates the effects of mycophenolate mofetil (MMF) on liver acceptance and rejection.

METHODS

Piebald Virol Glaxo rat livers were transplanted into Dark Agouti recipients, which spontaneously tolerate (TOL) the liver, or into Lewis recipients, which reject (REJ) the liver. MMF (40 mg/kg/day subcutaneously) was given for 5 days from days 0 to 4 (early) or from days 3 to 7 (late). In separate experiments, liver grafts were collected for assessment of infiltrate and of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma mRNA expression.

RESULTS

TOL liver transplants had a median survival time (MST) of more than 100 days (n=6), and neither early nor late MMF treatment of TOL transplants reduced survival (MST 85 days, P=0.19 and 78 days, P=0.08, respectively). Liver failure in most of these animals was the result of biliary problems, not rejection. There were few consistent differences between treated and untreated TOL animals in infiltrate or liver cytokine expression, although there was a moderate reduction in T-cell infiltrate in MMF-treated TOL animals (P=0.003 on day 5 TOL). In contrast, REJ transplants had an MST of 13 days (n=10), and early MMF treatment led to five of six animals surviving more than 100 days (P=0.0002), whereas late treatment was much less effective, with one of six animals surviving more than 100 days. REJ livers had significantly more IL-4 mRNA expression and immunoglobulin G1 deposition in the graft than TOL livers, and this was inhibited by early, but not late, MMF treatment.

CONCLUSIONS

MMF treatment inhibited rejection but not acceptance of liver allografts. Early administration was more effective in preventing rejection and demonstrated a more marked effect on IL-4 expression and alloantibody deposition than on graft T-cell infiltrate and expression of other cytokines.

"Infectious tolerance" develops after the spontaneous acceptance of Lewis-to-Dark Agouti rat liver transplants

BACKGROUND

After monoclonal antibody or donor-specific transfusion treatment, infectious tolerance to rat or mouse heart or skin transplants can be passed on to naive recipients by adoptive transfer of tolerant lymphocytes. We examined whether similar regulatory cells develop after the spontaneous acceptance of Lewis-to-Dark Agouti (DA) rat liver transplants without immunomodulating agents.

METHODS

After Lewis-to-DA rat liver transplantation, 100 x 10(6) splenocytes were harvested and adoptively transferred into a 450 rad-irradiated naive DA rat 24 hours before Lewis heart transplantation. Adoptive transfer of CD4+ or CD8+ T cells was also examined. In some experiments, splenocytes from recipients with long-term accepted Lewis hearts induced by adoptive transfer were serially transferred to multiple generations of recipients before Lewis rat heart transplantation. In vitro mixed lymphocyte culture response and cytotoxic T lymphocyte generation were measured.

RESULTS

When splenocytes from a DA rat recipient >60 days after Lewis rat liver acceptance were transferred into irradiated DA rat recipients, all Lewis rat hearts were accepted, whereas third-party Brown-Norway rat hearts were rejected. However, splenocytes from DA rat recipients 30 days after liver transplantation did not prolong Lewis rat heart survival. Adoptive transfer of 40 x 10(6) CD4+, 10 x 10(6) CD4+ or 10 x 10(6) CD8+ cells from a DA rat bearing Lewis rat liver >60 days resulted in acceptance of 88%, 80%, or 57% acceptance of Lewis rat hearts, respectively. Serial second and third adoptive transfer of long-term survivor splenocytes resulted in the acceptance of all Lewis rat hearts. In mixed lymphocyte culture, splenocytes from a naive DA rat and a DA rat accepting a Lewis rat liver transplant for >60 days showed similar proliferative responses to both Lewis and Brown-Norway rat stimulators. An equivalent level of indirect cytotoxic T lymphocyte activity was exhibited by splenocytes from both a naive DA and a DA rat accepting a Lewis rat liver transplant for >60 days.

CONCLUSIONS

Regulatory cells developing after the spontaneous acceptance of a Lewis to DA liver transplant can serially adoptively transfer the acceptance of a Lewis rat cardiac graft in spite of the presence of in vitro antidonor reactivity. Both CD4+ and CD8+ populations have this regulatory activity, although the CD4+ population plays the dominant role.

Intrathymic inoculation of donor liver specific antigen alleviates rejection of liver allotransplantation

Use and effects of liver specific antigen in orthotopic liver transplantations were researched in this study. Group I: syngeneic control (Wistar-to-Wistar); Group II: acute rejection (SD-to-Wistar); Group III: Thymic inoculation of SD rat LSA day 7 before transplantation. The observation of common situation and survival time, rejection grades, NF-KappaB activity of splenocytes and IL-2mRNA expression of grafted liver were used to analyze acute rejection severity and immune state of animals in different groups. The common situation of group I was very well after transplantation and no signs of rejection were found. Recipients of group II lost body weight progressively. All dead within day 9 to day 13 posttransplantation; median survival time was 10.7+/-0.51 days. It was an optimal acute rejection control. As for group III, 5 out of 6 recipients survived for a long time and common situation was remarkably better than that of group II. Its rejection grades were significantly lower than that of group II(P < 0.05). NF-KappaB activity was only detected in group I at day 5 and day 7 after transplantation, whereas high activity of NF-KappaB was detected at all time points in group II and the low NF-KappaB activity detected in group III was significantly lower than that of group II(P < 0.05). No IL-2mRNA expression was detected at any time point in group I, whereas high level expression was detected at all time points in group II and the low level expression only detected at day 3 in group III was significantly lower than that of group II(P < 0.05).

CONCLUSION

LSA is an important transplantation antigen which is involved directly in the immunorejection of liver transplantation. We report here for the first time that intrathymic inoculation of LSA can alleviate the rejection of liver allotransplantation; and that grafts can survive for a long time thereby, thus leading to a novel way to achieve liver transplantation immunotolerance.

Effect of 1,25-dihydroxyvitamin D3 on preventing allograft from acute rejection following rat orthotoic liver transplantation

AIM: To study the mechanism and the preventive role of 1, 25-dihydroxyvitamin D3 in acute rejection following orthotopic liver transplantation.

METHODS: Rats were randomly divided as donors or recipients for orthotopic liver allotransplantation model. Four groups were designed in the study, Group I: syngenic control (Wistar to Wistar); Group II: acute rejection (SD to Wistar); Group III: acute rejection treated with cyclosporine A, and Group IV: acute rejection treated with 1,25-(OH)₂ D₃. Liver function, rejection activity index and mRNA of IFN-γ, IL-10 intragraft in recipients were measured on day 1, 5, 7, 15, 30 posttransplant for assessing graft function, severity of acute rejection and immune state of recipients.

RESULTS: Survival time of recipients in Group IV was significantly prolonged (4/6 recipients survived for over 100 days. vs Group II, P < 0.001; vs Group III, P > 0.05). After treatment with 1,25-(OH)₂ D₃, mean value of all the assay tested on each experimental time was compared, liver function in group IV was significantly improved (AST 127 ± 41 U/L-360 ± 104 U/L, BIL 13 ± 5 mmol/l-38 ± 11 mmol/l; vs Group II, P < 0.05; vs Group III, P > 0.05. Rejection activity index was significantly decreased (0-3.3 ± 1.6; vs Group II, P < 0.05; vs Group III, P > 0.05). Level of hepatic IFN-γ mRNA in group IV was decreased, while level of hepatic IL-10 mRNA was increased (vs Group II, P < 0.05; vs Group III, P > 0.05).

CONCLUSION: Our results indicated that 1,25-(OH)₂ D₃ induced the secretion of cytokine toward to Th2 type, which would alleviate acute rejection, protect liver function and prolong survival of recipient after orthotopic liver transplantation.

Immunotolerance of liver allotransplantation induced by intrathymic inoculation of donor soluble liver specific antigen

AIM: To study the effects of liver specific antigen (LSA) on the immunoreaction of liver allotransplantation and its significance.

METHODS: Orthotopic liver transplantation was used in this study. Group I: syngeneic control (Wistar-to-Wistar); Group II: acute rejection (SD-to-Wistar). Group III: acute rejection treated by intramuscular injection of cyclosporine A (CsA) (SD-to-Wistar + CsA). Group IV: Intrathymic inoculation of SD rat LSA one week before transplantation (LSA + SD-to-Wistar). The common situation and survival time, rejection grades, NF-κB activity of splenocytes and intragraft cytokine gene expression were observed to analyze the acute rejection severity and immune state of animals.

RESULTS: The common situation of Wistar-to-Wistar group was very good after the transplantation and no signs of rejection were found. Recipients of SD-to-Wistar group lost body weight progressively. All died within 9 to 13 d after transplantation with the median survival time of 10.7 ± 0.51 d. It was an optimal control for acute rejection. The common situation of SD-to-Wistar + CsA group was bad during CsA medication but only with mild rejection. As for LSA + SD-to-Wistar group, 5 of 6 recipients survived for a long time and common situation was remarkably better than that of SD-to-Wistar group and SD-to-Wistar + CsA group. Its rejection grades were significantly lower than that of SD-to-Wistar group (P = 0.026). Furthermore, no significant discrepancies of rejection were found between SD-to-Wistar group and LSA + SD-to-Wistar group at day 7 and day 12 (P = 0.067). NF-κB activity, IFN-γ and IL-2mRNA expression were significantly inhibited in LSA + SD-to-Wistar group compared with that of SD-to-Wistar group (P < 0.05).

CONCLUSION: LSA is an important transplantation antigen which involves in the immunorejection of liver transplantation directly. We reported for the first time that intrathymic inoculation of LSA can induce immnotolerance of liver allotransplantation and grafts can survive for a long time thereby, thus leading to a novel way to liver transplantation immunotolerance.

Gene and cell therapies for diabetes mellitus: strategies and clinical potential

The last 5 years have witnessed an explosion in the use of genes and cells as biomedicines. While primarily aimed at cancer, gene engineering and cell therapy strategies have additionally been used for Mendelian, neurodegenerative and metabolic disorders. The main focus of gene and cell therapy strategies in metabolism has been diabetes mellitus. This disease is a disorder of glucose homeostasis, either due to the immune-mediated eradication of pancreatic beta cells in the islets of Langerhans (type 1 diabetes) or resulting from insulin resistance and obesity syndromes where the insulin-producing capability of the beta cell is ultimately exhausted in the face of insensitivity to the effects of insulin in the peripheral glucose-utilising tissues (type 2 diabetes). A significant number of animal studies have demonstrated the potential in restoring normoglycaemia by islet transplantation in the context of immunoregulation achieved by gene transfer of immunoregulatory genes to allo- and xenogeneic islets ex vivo. Additionally, gene and cell therapy has also been used to induce tolerance to auto- and alloantigens and to generate the tolerant state in autoimmune rodent animal models of type 1 diabetes or rodent recipients of allogeneic/xenogeneic islet transplants. The achievements of gene and cell therapy in type 2 diabetes are less evident, but seminal studies promise that this modality can be relevant to treat and perhaps prevent the underlying causes of the disease. Here we present an overview of the current status of gene and cell therapy for type 1 and 2 diabetes and we propose potential therapeutic options that could be clinically useful. For type 1 diabetes, transplantation of islets engineered to evade or suppress the recipient immune response is the most readily-available technology today. A number of gene delivery vectors encoding proteins that impair a variety of immune cells have already been examined and proven versatile. More challenging but, nonetheless, just over the horizon are attempts to promote tolerance to islet allografts. Type 2 diabetes will likely require a better understanding of the processes that determine insulin sensitivity in the periphery. Targeting tissues such as muscle and fat with vectors encoding genes whose products promote insulin sensitivity and glucose uptake is an approach that does not carry with it the side-effects often associated with pharmacologic agents currently in use. In the end, progress in vector design, elucidation of antigen-specific immunity and insulin sensitivity will provide the framework for gene drug use in the treatment of type 1 and type 2 diabetes.

A short course of cyclosporine immunosuppression inhibits rejection but not tolerance of rat liver allografts

BACKGROUND

Orthotopic liver transplants in many animal models are spontaneously accepted without requiring immunosuppression. Liver transplant acceptance is associated with early immune activation, and immunosuppressive drugs such as methylprednisolone inhibit acceptance. We investigated whether cyclosporine (CsA) inhibits rat liver transplant acceptance. We also examined the effects of CsA on infiltration and cytokine gene expression.

METHODS

Orthotopic liver transplantation was performed in the PVG donor to Dark Agouti recipient rat strain combination, which accepts the graft (tolerance; TOL), and in the PVG-to-Lewis combination, which rejects the graft in 9 to 16 days (rejection; REJ). CsA (1.5 mg/kg per day subcutaneously) was given to recipients for 5 days, starting from the day of transplantation to day 4 or from day 3 to day 7. In a separate experiment, transplanted livers were collected at days 1, 3, 5, and 7 after transplantation and examined for infiltration by immunohistochemistry and for expression of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma mRNA by quantitative reverse transcriptase-polymerase chain reaction.

RESULTS

Both early and delayed treatment with CsA significantly increased survival in the REJ strain combination, with a median survival time of 81 days and more than 100 days, respectively, compared with 13 days in the untreated group. Neither treatment affected survival of TOL animals, and all TOL groups had a median survival time of more than 100 days. Delayed treatment did not reduce survival; more animals survived for greater than 100 days after delayed treatment, although this did not reach significance ( P=0.08). T-cell infiltrate was inhibited in CsA-treated TOL animals compared with untreated animals at all times after treatment, whereas CD25 cells were only inhibited on day 3. CsA treatment of TOL grafts markedly reduced expression of IL-2, IL-4, and interferon-gamma compared with untreated recipients.

CONCLUSIONS

CsA did not significantly inhibit liver transplant acceptance and allowed some activation of T cells and CD25 expression but almost completely inhibited IL-2 and IL-4, which are required for survival of activated T cells.

Hepatic expression of IL-15 mRNA is associated with liver graft acceptance

BACKGROUND

Acute allograft rejection continues to be a major cause of morbidity following organ transplantation. The aim of this study was to investigate the local expression of a range of immunomodulatory molecules which may be mediating rejection of, or tolerance to, liver allografts.

METHODS

RNA was extracted from 31 protocol liver biopsies taken 7-10 days post-transplantation, reverse transcribed and screened by a sensitive RT-PCR for a wide range of cytokines and other immunomodulatory molecules. The mRNA profile of each biopsy was subsequently related to the histological and clinical status of the graft. Samples of RNA isolated from activated leukocytes and T cell clones, and from normal liver, were used as controls to compare to the 'immunological snapshot' obtained from the biopsies.

RESULTS

Presence of tumour necrosis factor-alpha, fas ligand, granzyme B and perforin mRNA in most of the liver biopsies reflected the occurrence of cell-mediated immune reactions. However, the expression of only one cytokine, interleukin-15 (IL-15), was significantly more frequent in allografts that showed no histological or biochemical signs of rejection during the early post-transplant period. Using an in vitro model it was demonstrated that recombinant IL-15 expands tenfold the number of CD3(+)CD56(+) (natural T; NT) cells from peripheral blood mononuclear cells cultures. Conditioning with IL-15 also increased cytotoxic activity of lymphocytes against leukaemic target cells.

CONCLUSIONS

Although considerable evidence for cell-mediated immunity was shown for all liver allografts, the only clinical association was for IL-15 mRNA expression and graft acceptance. An in vitro model suggested that IL-15 may be enhancing the numbers and the activity of local regulatory cells, in particular resident NT cells in the liver, which may have a role in killing activated lymphocytes such as graft-reactive host T cells.

Time course of upregulation of fibrogenic growth factors and cellular infiltration in a rodent model of chronic renal allograft rejection

BACKGROUND

Chronic Rejection (CR) is the leading cause of renal allograft dysfunction. Upregulation of growth factors has been shown in CR but the time point at which this occurs in not known. The aim of this study was to examine the time course of upregulation of growth factors and correlate this with the macrophage and myofibroblast interstitial infiltrate.

METHODS

Using a rat model of CR (F344 kidney donor to Lewis recipient), infiltration by ED1 + macrophages and proliferation of alpha-smooth muscle actin (alpha-SMA) and desmin-expressing cells was examined using immunohistochemistry. In addition, expression of mRNA for interferon-gamma (IFN-gamma), transforming growth factor-beta (TGF-beta), basic-fibroblast growth factor (b-FGF) and vascular endothelial growth factor (VEGF) was studied using a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) technique. Native Lewis rat kidney and Lewis-Lewis isografts were used as controls.

RESULTS

Immunohistochemical staining of ED1 + cells showed a marked increase in the macrophage infiltrate of allografts compared to isografts at all time periods (P = 0.0002) peaking at weeks 8-12 after transplantation. Expression of alpha-SMA was also increased in allografts (P = 0.002). RT-PCR analysis showed that mRNA for TGF-beta was maximally upregulated in allografts in comparison to isografts at week 8 after engraftment (P = 0.05) and declined thereafter, although remained at elevated levels compared to controls. IFN-gamma and b-FGF gene expression was increased in allografts late in the post-transplantation period.

CONCLUSION

Early infiltration of macrophages and production of TGF-beta1 was followed by later upregulation of fibrogenic growth factors and myofibroblasts associated with interstitial fibrosis and organ dysfunction.

Epithelial kinetics in mouse heterotopic tracheal allografts

Obliterative bronchiolitis (OB) is the most important cause of graft dysfunction post-lung transplantation. It is likely that the small airway epithelium is a target of the alloimmune response, and that epithelial integrity is a crucial determinant of airway patency. Our goals are to elucidate epithelial cell kinetics in the heterotopic mouse trachea model and to determine potential mechanisms of cell death in allografts. Allografts and isografts were obtained by transplanting BALB/c tracheas into C57BL/6 and BALB/c immunosuppressed and non-immunosuppressed hosts, respectively and harvested from day 3-20. Morphometry, BrdU and TUNEL labeling, and EM studies were performed. Columnar epithelium in isografts and allografts sloughs during day 0-3, but regenerates in both sets of grafts by day 10. Subsequently, allografts become inflamed and denuded, while isografts retain an intact epithelium. Prior to airway denudation, allografts exhibited significantly increased epithelial cell density, BrdU labeling index (LI), and TUNEL positive cells. Epithelial apoptosis was confirmed by electron microscopy. Allograft percent ciliated columnar epithelium and lumenal circumference were significantly decreased. Cyclosporin delayed airway fibrosis but did not alter the progression of the allograft through the phases of early ischemic injury, airway epithelial cell regeneration, and eventual cell death. These studies quantitatively demonstrate that the allograft epithelium actively regenerates in the alloimmune environment, but succumbs to increased apoptotic cell death, underscoring the importance of the airway epithelium as a self-renewing source of alloantigen.

Localized interleukin-10 gene transfer induces apoptosis of alloreactive T cells via FAS/FASL pathway, improves function, and prolongs survival of cardiac allograft

We hypothesized that localized IL-10 gene transfer can induce alloreactive T cell apoptosis and tested this hypothesis with liposome-mediated ex vivo intracoronary IL-10 gene transfer using a functional heterotopic allograft heart transplant model in rabbits. Localized IL-10 overexpression prolonged cardiac allograft survival over three folds. In parallel with the time-course of IL-10 overexpression, the percentage of apoptotic CD3+ cells among total CD3+ cells was significantly increased in the gene therapy group (36.5+/-3.9%) compared with that in the control group (6.2+/-2.6%, P<0.01) on postoperative day (POD) 3-6, and it was further increased (45.8+/-5.7%) on POD7-10. Apoptotic CD4+ and CD8+ cells were also significantly increased in the gene group (P<0.01). In contrast, the percentage of apoptotic myocytes significantly decreased from 10.1+/-0.8% in the control group to 3.5+/-0.4% in the gene group on POD7-10 (P<0.01). This reduction was inversely correlated with the increase in the percentages of apoptotic CD4+ and CD8+ cells (P<0.01). The percentage of caspase-3 positive myocytes was significantly reduced, although percentages of caspase-3 positive CD4+ and CD8+ cells were markedly increased in the gene group (P<0.01). Moreover, about 60-80% of apoptotic T lymphocytes expressed Fas in the gene group compared with less than 10% in the control group (P<0.01). These results suggest that localized IL-10 gene transfer induces alloreactive T cell apoptosis via the Fas/FasL pathway that may contribute to the alleviated acute rejection, improved cardiac function, and prolonged survival in the IL-10 gene-treated cardiac allografts.

Postoperative administration of donor B cells induces rat kidney allograft acceptance: lack of association with Th2 cytokine expression in long-term accepted grafts

BACKGROUND

Although donor leukocytes are only thought to prolong survival when administered before transplantation, recent evidence shows that they are effective at transplantation. This study aims to identify the leukocyte subset that is most active in prolonging kidney allograft survival and examine the cytokine expression in long-term acceptance.

METHODS

PVG rat kidneys were transplanted to completely MHC class I and class II-mismatched DA recipients. Donor B cells or T cells, purified by negative selection, were injected i.v. at the time of transplantation. Expression of interleukin (IL)-2, IL-4, IL-10, interferon (IFN)-gamma, and transforming growth factor-beta mRNA was measured by quantitative real-time polymerase chain reaction (PCR). Immunohistochemical analysis and terminal deoxynucleotide transferase-mediated dUTP nick-end labelling (TUNEL) staining was used to identify infiltrating cells and apoptotic cells, respectively, in sections of kidney allografts.

RESULTS

Median kidney graft survival time (MST) of B cell-treated animals (n=5) was >300 days, compared with 7 days in untreated animals (n=7) (P=0.003), whereas animals treated with the same number of T cells (n=6) had a MST of 17 days (P=0.1 vs. untreated, P=0.03 vs. B cell-treated). Examination of the long-term (>300 days) accepted grafts from B cell-treated recipients showed little evidence of kidney damage but a moderate perivascular infiltrate consisting of T and B cells. This infiltrate seemed to be quiescent because there was no detectable expression of IL-2 receptors or of apoptotic cells. It produced little or no cytokine mRNA, because expression in the long-term accepted grafts was similar to levels in normal kidneys or syngeneic transplants. There was a marked increase of cytokine mRNA early after transplantation in both leukocyte-treated and untreated grafts, with more rapid appearance of IFN-gamma and IL-10 in leukocyte-treated grafts.

CONCLUSIONS

Donor B cells efficiently induce long-term acceptance of transplanted kidneys in a fully MHC-mismatched rat model when administered at transplantation, by a mechanism that seems to be independent of Th2 cytokine expression within the long-term accepted graft.

Spontaneous acceptance of liver transplants in rodents: evidence that liver leucocytes induce recipient T-cell death by neglect

In many animal models transplanted livers are not rejected, even when there is a complete MHC mismatch between the donor and recipient and the recipient is not immunosuppressed. This distinguishes liver transplants from other organs, such as kidneys and hearts, which are rapidly rejected in mismatched individuals. Acceptance of transplanted livers in a rat model is not due to the absence of an immune response to the liver and there is a rapid, abortive response that is ultimately exhausted. Donor leucocytes transferred with the liver appear to be responsible for both liver acceptance and the abortive activation of the recipient's T cells. The immune mechanism of liver transplant acceptance appears to be due to 'death by neglect' in which T cells are activated to express IL-2 and IFN-gamma mRNA in the recipient lymphoid tissues, but not at adequate levels within the graft. Subsequently the activated T cells die leading to specific clonal deletion of liver donor-reactive T cells. These findings have important implications for liver transplant patients as immunosuppressive drugs that are given to prevent rejection can also interfere with this form of tolerance. In addition, it might be possible to modify the immunosuppressive drug treatment of transplant patients to promote the process of death by neglect of recipient alloreactive T cells.

Antigenic load and peripheral chimeric levels in entire and partial liver allograft recipients

Orthotopic partial liver transplantation (PLT) models were developed in rats to explore the unique role of the liver in transplant tolerance. In PVG rats, syngeneic PLT established that surgical reduction to one-third of the liver and orthotopic transplantation permitted survival. Allogeneic PLT in the PVG to DA liver-tolerant model, both 50% and 33%, did not affect the tolerogeneic property of the liver, with all PLT recipients surviving indefinitely. Blood samples taken at various time points for detection of donor cells using flow cytometry showed a steady increase in donor cell chimerism in both PLT and whole liver transplantation (WLT) recipients that persisted throughout the 3-month observation period. At each time point, the level of donor cell chimerism in PLT was higher than that in WLT. We conclude that transplantation of one-third of the liver is compatible with survival in rats. Reduction of antigenic load by means of hepatectomy does not affect the tolerogenic effect of the liver in the PVG to DA LT model because of the remarkable regeneration capability of the liver. Peripheral chimeric levels increase progressively after WLT, suggesting that this is an ongoing immunological phenomenon. The earlier and increased chimerism after PLT may be associated with liver regeneration.

Weaning of immunosuppression in living donor liver transplant recipients

BACKGROUND

Some reported studies have indicated the possibility of immunosuppression withdrawal in cadaveric liver transplantation. The aim of this study was to evaluate the possibility and feasibility of weaning living donor liver transplant recipients from immunosuppression.

METHODS

From June of 1990 to October of 1999, 63 patients were considered to be weaned from immunosuppression. They consisted of 26 electively weaned patients and 37 either forcibly or incidentally weaned patients (nonelective weaning) due to various causes but mainly due to infection. Regarding elective weaning, we gradually reduced the frequency of tacrolimus administration for patients who survived more than 2 years after transplantation, maintained a good graft function, and had no rejection episodes in the preceding 12 months. The frequency of administration was reduced from the conventional b.i.d. until the start of weaning to q.d., 4 times a week, 3 times a week, twice a week, once a week, twice a month, once a month, and finally, the patients were completely weaned off with each weaning period lasting from 3 to 6 months. The reduction method of nonelective weaning depended on the clinical course of each individual case. When the patients were clinically diagnosed to develop rejection during weaning, then such patients were treated by a reintroduction of tacrolimus or an additional steroid bolus when indicated.

RESULTS

Twenty-four patients (38.1%) achieved a complete withdrawal of tacrolimus with a median drug-free period of 23.5 months (range, 3-69 months). Twenty-three patients (36.5%) are still being weaned at various stages. Sixteen patients (25.4%) encountered rejection while weaning at median period of 9.5 months (range, 1-63 months) from the start of weaning. All 16 were easily treated with the reintroduction of tacrolimus or additional steroid bolus therapy.

CONCLUSIONS

We were able to achieve a complete withdrawal of immunosuppression in some selected patients. Although the mechanism of graft acceptance in these patients has yet to be elucidated, we believe that a majority of long-term patients undergoing living donor liver transplantation may, thus, be potential candidates to be successfully weaned from immunosuppression.

A short course of methylprednisolone immunosuppression inhibits both rejection and spontaneous acceptance of rat liver allografts

BACKGROUND

The effects of immunosuppressive drugs on transplant tolerance have not been extensively studied, although their effect on rejection is well established.

METHODS

We examined the effects of a short course of treatment with the immunosuppressive drug methylprednisolone (MP) on the survival of PVG liver allografts in Dark Agouti (DA) recipients that accepted the livers and in Lewis recipients that rejected the livers. Infiltration of liver allografts was examined by immunohistochemical staining of liver sections, and apoptosis was measured by terminal deoxynucleotide transferase-mediated dUTP nick end labeling.

RESULTS

A 5-day course of MP (days 0 to 4) led to rejection of four of six livers (mean survival time [MST] 99 days) in DA recipients compared with long-term survival (MST >100 days) in untreated animals. Delayed administration of MP (days 3 to 7) exacerbated rejection in DA recipients, and all eight animals rejected the graft (MST 68.5 days). Treatment of Lewis recipients with MP did not significantly prolong survival when administered from days 0 to 4 (MST 13 days), although delay of administration improved the outcome. Treatment from days 3 to 7 resulted in an MST of 21 days, whereas treatment from days 7 to 11 resulted in an MST of 41.5 days. MP treatment from day 3 to day 7 reduced T cells and interleukin 2 receptor-expressing cells but increased the numbers of apoptotic cells infiltrating both DA and Lewis strain allografts.

CONCLUSIONS

These results show that immunosuppression with MP inhibits both spontaneous tolerance and rejection of liver allografts in a rat model and question the efficacy of administering MP to all liver allograft recipients from the time of transplantation.

Persistence of stable intragraft cell chimerism in rat liver allografts after drug-induced tolerance

BACKGROUND

Drug-induced tolerance of rat liver allografts is well documented. We analyzed cellular events during immunosuppressive therapy on day (d) 10 and in the late phase (d 100) after transplantation to assess for characteristics in the intrahepatic leukocyte (IHL) population in the phase of tolerance.

METHODS

Lewis rats served as recipients of Dark Agouti rat livers. Temporary immunosuppression with either cyclosporine (CsA) monotherapy (3 mg/kg/d) or triple therapy that consisted of a subtherapeutic CsA dosage (0.25 mg/kg/d) and monoclonal antibodies directed against the interleukin-2 receptor (IL-2R, CD25) and the intercellular adhesion molecule-1 (ICAM-1, CD54) was administered from postoperative d 0 to d 13. Cell migration and cell activation within liver grafts was assessed by standard histology and flow cytometry. IHL apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL).

RESULTS

Both CsA monotherapy and triple therapy prolonged liver allograft survival to more than 100 d and led to the induction of donor-specific tolerance. Untreated recipients rejected their allografts within 14 d. In both groups, donor-specific IHLs initially dropped to 18% to 25% on d 10, but they rebounded to as much as 40% on d 100 as a common characteristic of both groups. Within this population, donor-specific T cells were dominant. In both groups, increased numbers of activated (IL-2R+) CD8+ T lymphocytes were present on d 100. No accumulation of apoptotic IHL was observed on d 100. Their proportion was unchanged in the triple therapy group and slightly decreased in the CsA group compared to the syngeneic controls.

CONCLUSIONS

The present study reveals that tolerant liver allografts are repopulated by donor-specific T lymphocytes. This phenomenon is independent of the type of applied immunosuppression. The persistence of activated CD8+ T cells in the phase of proven donor-specific tolerance on d 100 indicates that liver tolerance is associated with the state of a permanent intragraft immune activation. It seems that the coexistence of donor cells with infiltrating recipient cells within liver grafts, termed intrahepatic cell chimerism, is characteristic for tolerated liver allografts.

Posttransplant administration of donor leukocytes induces long-term acceptance of kidney or liver transplants by an activation-associated immune mechanism

Donor leukocytes play a dual role in rejection and acceptance of transplanted organs. They provide the major stimulus for rejection, and their removal from the transplanted organ prolongs its survival. Paradoxically, administration of donor leukocytes also prolongs allograft survival provided that they are administered 1 wk or more before transplantation. Here we show that administration of donor leukocytes immediately after transplantation induced long-term acceptance of completely MHC-mismatched rat kidney or liver transplants. The majority of long-term recipients of kidney transplants were tolerant of donor-strain skin grafts. Acceptance was associated with early activation of recipient T cells in the spleen, demonstrated by a rapid increase in IL-2 and IFN-gamma at that site followed by an early diffuse infiltrate of activated T cells and apoptosis within the tolerant grafts. In contrast, IL-2 and IFN-gamma mRNA were not increased in the spleens of rejecting animals, and the diffuse infiltrate of activated T cells appeared later but resulted in rapid graft destruction. These results define a mechanism of allograft acceptance induced by donor leukocytes that is associated with activation-induced cell death of recipient T cells. They demonstrate for the first time that posttransplant administration of donor leukocytes leads to organ allograft tolerance across a complete MHC class I plus class II barrier, a finding with direct clinical application.