CD40L (CD154) expression in human liver allografts during chronic ductopenic rejection

Basic Understanding of Liver Transplant Immunology

The liver is a specialized organ and plays an important role in our immune system. The liver constitutes parenchymal cells which are hepatocytes and cholangiocytes (60-80%) and non-parenchymal cells like liver sinusoidal endothelial cells (LSECs), hepatic satellite/Ito cells, Kupffer cells, neutrophils, mononuclear cells, T and B lymphocytes (conventional and non-conventional), natural killer cells, and natural killer T (NKT) cells. The liver mounts a rapid and strong immune response, under unfavorable conditions and acts as an immune tolerance to a variety of non-pathogenic antigens. This delicate and dynamic interaction between different kinds of immune cells in the liver maintains a balance between immune screening and immune tolerance. The liver allografts are privileged immunologically; however, allograft rejection is not uncommon and is classified as cell or antibody-mediated. Advancements in transplant immunology help in the prevention of allografts rejection by immune reactions of the host thus leading to better graft and host survival. Fewer patients may not require immunosuppression due to systemic donor-specific T-cell tolerance. The liver tolerance mechanism is poorly studied, and LSEC and unconventional lymphocytes play an important role that dampens T cell response either by inducing apoptosis of cells or inhibiting co-stimulatory pathways. Newer cell-based therapy based on Treg, dendritic cells, and mesenchymal stromal cells will probably change the future of immunosuppression. Various invasive and non-invasive biomarkers and artificial intelligence have also been investigated to predict graft survival, post-transplant complications, and immunotolerance in the future.

The immunophenotype of antigen presenting cells of the mononuclear phagocyte system in normal human liver--a systematic review

The mononuclear phagocytic system (MPS), comprised of monocytes, macrophages, and dendritic cells, is essential in tissue homeostasis and in determining the balance of the immune response through its role in antigen presentation. It has been identified as a therapeutic target in infectious disease, cancer, autoimmune disease and transplant rejection. Here, we review the current understanding of the immunophenotype and function of the MPS in normal human liver. Using well-defined selection criteria, a search of MEDLINE and EMBASE databases identified 76 appropriate studies. The majority (n=67) described Kupffer cells (KCs), although the definition of KC differs between sources, and little data were available regarding their function. Only 10 papers looked at liver dendritic cells (DCs), and largely confirmed the presence of the major dendritic cell subsets identified in human blood. Monocytes were thoroughly characterized in four studies that utilized flow cytometry and fluorescent microscopy and highlighted their prominent role in liver homeostasis and displayed subtle differences from circulating monocytes. There was some limited evidence that liver DCs are tolerogenic but neither liver dendritic cell subsets nor macrophages have been thoroughly characterized, using either multi-colour flow cytometry or multi-parameter fluorescence microscopy. The lobular distribution of different subsets of liver MPS cells was also poorly described, and the ability to distinguish between passenger leukocytes and tissue resident cells remains limited. It was apparent that further research, using modern immunological techniques, is now required to accurately characterize the cells of the MPS in human liver.

Immunology of liver transplantation

In comparison with other solid-organ transplants, liver allografts are immunologically privileged. Allografts are rejected by immune reactions of the host, and clinical therapy for liver allografts includes immunosuppression to prevent rejection. Orthotopic liver transplant causes systemic donor-specific T-cell tolerance. In addition, antigens introduced into hepatocytes or the portal vein cause tolerance. The basic mechanism in liver tolerance may include continuous exposure of diverse liver cell types to endotoxin derived from intestinal bacteria. This exposure promotes the expression of cytokines, antigen-presenting molecules, and costimulatory signals that inactivate T cells, partly by effects on liver antigen-presenting cells. A simple, reliable, noninvasive assay to evaluate antidonor alloreactivity may be important in implementing these approaches in the laboratory and clinic.

Diagnosis, pathogenesis, and treatment of autoimmune hepatitis after liver transplantation

Autoimmune hepatitis can recur or appear de novo after liver transplantation, and it can result in hepatic fibrosis, graft loss, and re-transplantation. The goals of this review are to describe the prevalence, manifestations, putative pathogenic mechanisms, outcomes, and management of these occurrences. Autoimmune hepatitis recurs in 8-12 % of transplanted patients at 1 year and 36-68 % at 5 years. Recurrence may be asymptomatic and detected only by surveillance liver test abnormalities or protocol liver tissue examination. Autoantibodies that characterized the original disease, hypergammaglobulinemia, increased serum immunoglobulin G level, and histological findings of interface hepatitis, lymphoplasmacytic infiltration, perivenular hepatocyte necrosis, pseudo-rosetting, and acidophil bodies typify recurrence. Premature corticosteroid withdrawal and pre-transplant severity of the original disease are possible risk factors. De novo autoimmune hepatitis occurs in 1-7 % of patients 0.1-9 years after transplantation, especially in children. The appearance of autoantibodies may herald its emergence, and antibodies to glutathione-S-transferase T1 have been predictive of the disease. Recurrent disease may reflect recruitment of residual memory T lymphocytes and host-specific genetic predispositions, whereas de novo disease may reflect an allo-antigenic immune response and molecular mimicries that override self-tolerance. Treatment should be appropriate for autoimmune hepatitis and not based on anti-rejection drugs. Corticosteroid therapy alone or combined with azathioprine is the essential treatment. The substitution of mycophenolate mofetil for azathioprine and switch of the calcineurin inhibitor or its replacement with rapamycin have also been used for refractory disease. Re-transplantation has been necessary in 8-23 %.

Zinc finger protein A20 protects rats against chronic liver allograft dysfunction

AIM: To investigate the effect of zinc finger protein A20 on chronic liver allograft dysfunction in rats.

METHODS: Allogeneic liver transplantation from DA rats to Lewis rats was performed. Chronic liver allograft dysfunction was induced in the rats by administering low-dose tacrolimus at postoperative day (POD) 5. Hepatic overexpression of A20 was achieved by recombinant adenovirus (rAd.)-mediated gene transfer administered intravenously every 10 d starting from POD 10. The recipient rats were injected with physiological saline, rAdEasy-A20 (1 × 10⁹ pfu/30 g weight) or rAdEasy (1 × 10⁹ pfu/30 g weight) every 10 d through the tail vein for 3 mo starting from POD 10. Liver tissue samples were harvested on POD 30 and POD 60.

RESULTS: Liver-transplanted rats treated with only tacrolimus showed chronic allograft dysfunction with severe hepatic fibrosis. A20 overexpression ameliorated the effects on liver function, attenuated liver allograft fibrosis and prolonged the survival of the recipient rats. Treatment with A20 suppressed hepatic protein production of tumor growth factor (TGF)-β1, interleukin-1β, caspase-8, CD40, CD40L, intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and E-selectin. A20 treatment suppressed liver cell apoptosis and inhibited nuclear factor-κB activation of Kupffer cells (KCs), liver sinusoidal endothelial cells (LSECs) and hepatic stellate cells (HSCs), and it subsequently decreased cytokine mRNA expression in KCs and LSECs and reduced the production of TGF-β1 in HSCs.

CONCLUSION: A20 might prevent chronic liver allograft dysfunction by re-establishing functional homeostasis of KCs, LSECs and HSCs.

Posttransplant plasma cell hepatitis (de novo autoimmune hepatitis) is a variant of rejection and may lead to a negative outcome in patients with hepatitis C virus

De novo autoimmune hepatitis has been described in both pediatric and adult liver transplantation (LT) recipients. Studies of small numbers of patients have proposed it to be an alloimmune hepatitis or form of chronic rejection. We have recently noted an increasing number of patients with post-LT recurrent hepatitis C virus (HCV) developing this, with an apparent negative impact on outcome and survival. We term this entity posttransplant plasma cell hepatitis (PCH). A search of our institution's pathology database was performed with the terms "plasma cell(s)," "lymphoplasmacytic infiltrate," and "liver allograft." A histological scoring system was devised to more reliably diagnose PCH in the setting of recurrent HCV. Thirty-eight patients were identified, and their clinical data were analyzed. Sixty percent had a negative outcome as defined by the development of cirrhosis, need for retransplantation, or death. Eighty-two percent had recent lowering of immunosuppression or subtherapeutic calcineurin inhibitor levels; 58% developed PCH within 2 years post-LT. Histologic resolution of PCH was associated with good outcome (P < 0.001). Patients not receiving treatment had a negative outcome (P = 0.007) as did patients receiving corticosteroids as therapy (P = 0.02). Persistence (P = 0.007) or recurrence of PCH was associated with negative outcome. In conclusion, PCH is a histologic variant of rejection. On liver biopsy, PCH can at times be difficult to diagnose, and the use of a standardized scoring system is recommended to differentiate it from other forms of allograft dysfunction. Treatment by optimization of immunosuppression without the use of corticosteroids appears effective. The development of PCH in the setting of recurrent HCV is a negative prognostic factor for patient outcome and allograft failure.

Transplantation immunology: what the clinician needs to know for immunotherapy

The liver is unique among transplanted organs with respect to its interaction with the host immune system. There is evidence, both anecdotal and documented, that some liver recipients who cease taking immunosuppressive drugs maintain allograft function, suggesting robust tolerance is in place. Moreover, recipients of human liver allografts require less immunosuppression than do other organ recipients, and liver transplants confer protection on other organ grafts from the same donor. Hence, the liver shows features of immune privilege. Still, the liver can display destructive immunologic processes such as rejection in approximately one quarter of patients. The understanding of the cellular and molecular mechanisms operant in tolerance vs allograft rejection is important for developing new agents to improve long-term outcome, minimize infectious complications (including recurrence of hepatotropic viruses), and deliver immunosuppression without long-term toxicity. This review describes the unique aspects of the hepatic immune response, the pathways involved in T-cell activation and alloantigen recognition, effector cells and pathways mediating liver allograft rejection, the role of regulatory T cells, and targets of current and future immunosuppressive agents.

CD40L proinflammatory and profibrotic effects on proximal tubular epithelial cells: role of NF-kappaB and lyn

Chronic allograft nephropathy (CAN) is the main cause of renal graft loss, but its pathogenic mechanisms are still unclear. Immune system activation has been suggested as a key event in the development of CAN. CD40 is a co-stimulatory protein whose expression is upregulated in proximal tubular epithelial cells (PTEC) in acute rejection. This receptor interacts with CD40L, expressed by activated T cells. CD40L induces the production by PTEC of different proinflammatory cytokines, but very little is known of its profibrotic effects. The aim of this study was to investigate the effect of CD40/CD40L interaction on PTEC expression of plasminogen activator inhibitor-1 (PAI-1), a powerful profibrotic mediator, and monocyte chemoattractant protein-1 (MCP-1), a proinflammatory cytokine, and to investigate the signaling pathways that lead to these effects. Soluble CD40L induced a time-dependent increase in both PAI-1 and MCP-1 gene expression and protein production in PTEC. CD40 cross-linking on PTEC caused TNF-R-associated factors 2 and 6 membrane translocation. This event led to NF-kappaB activation, through the NF-kappaB-inducing kinase, and to a significant increase in the phosphorylation of lyn, a src-related tyrosine kinase. Lyn, upon phosphorylation, became strictly associated with caveolin-1, a scaffolding protein enriched in caveolae. Lyn inhibition did not have any effect on CD40L-induced NF-kappaB activation and MCP-1 expression but abolished PAI-1 induction. On the contrary, NF-kappaB inhibition significantly reduced only MCP-1 expression. In conclusion, CD40L could play a key role in the pathogenesis of CAN through PAI-1 induction. CD40L profibrotic and proinflammatory effects are mediated by different signaling pathways, suggesting that drugs that inhibit inflammation may not be equally effective in reducing fibrosis.

Assessment of serum matrix metalloproteinases MMP-2 and MMP-9 after human liver transplantation: increased serum MMP-9 level in acute rejection

BACKGROUND

Alterations in synthesis and breakdown of extracellular matrix components play a role in acute rejection after orthotopic liver transplantation (OLT). Matrix metalloproteinases (MMPs) are capable of degrading basement membranes and are involved in the process of tissue remodelling in inflammation and liver fibrosis.

METHODS

We examined MMP-2 and MMP-9 in serum of 33 patients before and during 1 year after OLT, in 60 controls as well as in some specimens of cirrhotic liver and control liver tissue.

RESULTS

Serum MMP-2 levels before OLT were significantly higher compared with controls and decreased approximately 50% after OLT. Also, the MMP-2 content of cirrhotic liver specimens was significantly higher compared with normal liver. MMP-9 in serum and liver tissue of patients were similar to controls, but serum levels showed a peak at 1 week after OLT. At this time-point, total and active/inhibitor-complexed MMP-9 was significantly higher in patients with rejection (n=13) compared with those without rejection (n=20). The relative amount of MMP-9 in the active/inhibitor-complexed form did not differ between each group over time. Immunohistochemical staining at 1 week after OLT showed increased numbers of MMP-9-positive inflammatory cells in the portal triads of patients with rejection.

CONCLUSIONS

Patients with acute allograft rejection have elevated serum levels of MMP-9 1 week after OLT, which was most likely derived from inflammatory cells. An increased MMP-2 serum level and liver tissue content was found in patients with cirrhosis, which decreased after OLT. These observations indicate active involvement of MMP-2 and -9 in end-stage liver disease and OLT.

The role of B cells and alloantibody in the host response to human organ allografts

Some human organ transplants deteriorate slowly over a period of years, often developing characteristic syndromes: transplant glomerulopathy (TG) in kidneys, bronchiolitis obliterans in lungs, and coronary artery disease in hearts. In the past, we attributed late graft deterioration to "chronic rejection", a distinct but mysterious immunologic process different from conventional rejection. However, it is likely that much of chronic rejection is explained by conventional T-cell-mediated rejection (TMR), antibody-mediated rejection (AMR), and other insults. Recently, criteria have emerged to now permit us to diagnose AMR in kidney transplants, particularly C4d deposition in peritubular capillaries and circulating antibody against donor human leukocyte antigens (HLA). Some cases with AMR develop TG, although the relationship of TG to AMR is complex. Thus, a specific diagnosis of AMR in kidney can now be made, based on graft damage, C4d deposition, and donor-specific alloantibodies. Criteria for AMR in other organs must be defined. Not all late rejections are AMR; some deteriorating organs probably have smoldering TMR. The diagnosis of late ongoing AMR raises the possibility of treatment to suppress the alloantibody, but efficacy of the available treatments requires further study.

Analysis of intragraft gene and protein expression of the costimulatory molecules, CD80, CD86 and CD154, in orthotopic liver transplant recipients

CD40-CD154 and/or CD28-CD80/86 costimulatory blockade induces long-term allograft survival in numerous animal models. Studies examining the expression of costimulatory molecules during acute cellular rejection (ACR) have been limited to renal and cardiac allografts. The aim of this study was to describe the relationship between intragraft costimulatory molecule expression in OLT recipients and ACR. Forty-five liver biopsies were obtained at reperfusion and day 7. Gene and protein expression of CD80, CD86 and CD154 were analyzed by RT-PCR and immunohistochemistry. CD154 protein expression was present in 13 of 18 patients with a RAI score of 4, but in only two of 14 patients with a RAI score of <4. There was a strong association between the RAI score and the presence of CD80 and CD154 immunoreactivity. CD86 protein expression did not correlate with the severity of ACR. In reperfusion biopsies CD154, but not CD80 or CD86, protein expression correlated with the total ischaemic time. There was no association between expression of costimulatory molecule genes and ACR. In conclusion, we have demonstrated an association between CD154 and CD80 protein expression and ACR in orthotopic liver allografts.

Functional CD40 expression induced following bacterial infection of mouse and human osteoblasts

Bacterially induced bone infections often result in significant local inflammatory responses which are coupled with loss of bone. However, the mechanisms necessary for the protective host response, or those responsible for pathogen-induced bone loss, are not clear. Recent evidence demonstrates that bacterially infected osteoblasts secrete chemokines and cytokines, suggesting that these cells may have an unappreciated role in supporting localized inflammation. In this study, mouse and human osteoblasts were investigated for their ability to express functional CD40 upon exposure to two important pathogens of bone, Staphylococcus aureus and Salmonella enterica serovar Dublin. Bacterial infection of cultured mouse or human osteoblasts resulted in increased CD40 mRNA and CD40 protein expression induced by either pathogen. Importantly, CD40 expression by osteoblasts was functional, as assessed by ligation of this molecule with recombinant, soluble CD154. CD40 activity was assessed by induction of interleukin-6 and granulocyte-macrophage colony-stimulating factor in osteoblasts following ligation. Cocultures of activated CD4(+) T lymphocytes and osteoblasts could interact via CD40 and CD154, since an antibody against CD40 could block macrophage inflammatory protein-1alpha secretion. Taken together, these studies conclusively demonstrate that infected osteoblasts can upregulate expression of functional CD40 molecules which mediate cytokine secretion. This surprising result further supports the notion that bone-forming osteoblasts can directly interact with CD154-expressing cells (i.e., T lymphocytes) and can contribute to the host response during bone infection.

CD40 expressed by human brain endothelial cells regulates CD4+ T cell adhesion to endothelium

Recent evidence suggests that interactions between CD40 on antigen presenting cells (APC) and CD40L on T cells generate signals that result in the activation of APC. In this study, the expression and function of CD40 was investigated in primary cultures of human brain microvessel endothelial cells (HBMEC). Results revealed constitutive expression of CD40 on untreated HBMEC. Stimulation with TNF-alpha, IFN-gamma, LPS or combination of TNF-alpha and IFN-gamma significantly upregulated CD40. The majority of CD40 molecules were localized on the apical surface of EC. Incubation of HBMEC with soluble CD40L resulted in increased expression of the adhesion molecules E-selectin, VCAM-1 and ICAM-1. Consequently, the adhesion of both resting and anti-CD3 activated CD4+ T lymphocytes to CD40L treated HBMEC was significantly increased compared to unstimulated EC. The expression of CD40 by cerebral endothelium, and endothelial cell activation following binding of CD40 to its ligand, CD40L, suggest a potential mechanism by which activated CD40L expressing T cells could enhance adhesion and migration of inflammatory cells across the blood-brain barrier (BBB) to sites of inflammation in the human central nervous system (CNS).

Oxidized low-density lipoprotein augments and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors limit CD40 and CD40L expression in human vascular cells

BACKGROUND

Although CD40 signaling participates in atherosclerosis, links between lipid risk factors and this inflammatory pathway remain obscure. Cardiovascular risk reduction by 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) may involve actions beyond lipid lowering, including reduced inflammation. Therefore, this study analyzed whether oxidized low-density lipoprotein (oxLDL) induces CD40/CD40L expression on cells implicated in atherogenesis and whether statins affect their expression in vitro as well as the expression of soluble CD40L (sCD40L) in vivo.

METHODS AND RESULTS

Treatment of human vascular endothelial and smooth muscle cells and mononuclear phagocytes with oxLDL augmented the basal expression of CD40 and CD40L mRNA and protein. In contrast, cerivastatin, atorvastatin, or simvastatin concentration-dependently diminished the constitutive as well as oxLDL- or cytokine-induced expression of the receptor/ligand dyad, an effect reversed by mevalonate. Patients treated with statins had diminished sCD40L plasma levels compared with untreated control patients (8.3+/-3.1 ng/mL [n=11] versus 13.1+/-2.5 ng/mL [n=16], P<0.05), supporting the clinical relevance of the in vitro observations. Platelet-enriched plasma of mice deficient in CD40L showed markedly delayed fibrin clot formation, suggesting a role for the ligand in blood coagulation and supporting the hypothesis that statin-mediated reduction in CD40/CD40L expression might limit thrombosis.

CONCLUSIONS

OxLDL may promote expression of CD40 and CD40L in human atheroma. Statins may limit the expression of the CD40 receptor/ligand dyad in two ways, directly as well as through diminished lipoprotein levels. Thus, reduced CD40 signaling may account for some of the statins' antiinflammatory action.

Autoimmune hepatitis after liver transplantation and other lessons of self-intolerance

Autoimmune hepatitis has been described as recurrent or de novo disease after transplantation. The legitimacy of these diagnoses and the bases for their occurrence are unknown. To better understand these aspects of allograft dysfunction, the purported pathogenic mechanisms of classical autoimmune hepatitis were reviewed and extrapolated to recurrent and de novo disease after transplantation. Loss of self-tolerance may relate to defects in the negative selection of autoreactive immunocytes and the clonal expansion of promiscuous lymphocytes that are cross-reactive to homologous antigens (molecular mimicry). Repopulation of the allograft with recipient antigen-presenting cells and the presence of primed promiscuous cytotoxic T cells within the recipient are likely factors for recurrent disease. Targets may be the same peptides that triggered the original disease, donor-derived class II antigens of the major histocompatibility complex, or homologous antigens associated with unidentified hepatotrophic viruses. De novo disease is probably due to similar mechanisms, but its predilection for children suggests that thymic dysfunction associated with cyclosporine treatment may be a factor. Corticosteroid therapy is effective in each condition. In conclusion, recurrent and de novo autoimmune hepatitis after transplantation are examples of self-intolerance. The mechanisms that perturb immunologic homeostasis in this human model of the classical disease must be studied more rigorously.

Costimulatory blockade prevents early rejection, promotes lymphocyte apoptosis, and inhibits the upregulation of intragraft interleukin-6 in an orthotopic liver transplant model in the rat

Costimulatory pathways have a pivotal role in the T-cell response to alloantigen. The role of costimulatory blockade with anti-CD154 in orthotopic liver transplantation (OLT) has not been examined previously. This study aims to investigate effects of anti-CD154 and CTLA4-immunoglobulin (Ig) in the early post-OLT period using a major histocompatibility complex-disparate fully arterialized OLT model in the rat. Lewis rats underwent OLT with Dark Agouti liver allografts. Recipients were randomized to receive (1) isotype control, (2) anti-CD154, (3) CTLA4-Ig, or (4) cyclosporine A (CyA). Rats were killed day 8, and specimens were obtained for histological examination, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling, immunohistochemistry, and quantitative reverse-transcriptase polymerase chain reaction. An additional five transplant recipients were treated with anti-CD154 for 14 days postoperatively to assess long-term allograft survival. All isotype control animals died on or before day 6 of acute rejection. Apart from four deaths caused by nonimmunologic causes, all treated recipients survived to day 8. The median survival of rats treated for 14 days with anti-CD154 was greater than 150 days. Serum aspartate aminotransferase and bilirubin levels normalized by day 3 in the CyA group and day 5 in transplant recipients treated with costimulatory blockade. Histologically, there was no difference between isotype controls and CTLA4-Ig-treated animals, whereas anti-CD154-treated transplant recipients had a lower Banff score. CD4+ and CD8+ T-cell infiltrates were prominent in transplant recipients treated with costimulatory blockade. Intragraft analysis showed an increase in lymphocyte apoptosis, Fas ligand messenger RNA expression, and reduction in interleukin-6 gene expression in transplant recipients treated with costimulatory blockade. Costimulatory blockade did not alter intragraft gene expression of other mediators of T-cell priming, differentiation, and effector function compared with isotype control animals. In conclusion, costimulatory blockade prevented acute rejection, enabled long-term survival, and increased intragraft lymphocyte apoptosis in a high-responding rat OLT model.

Co-stimulatory blockade and tolerance induction in transplantation

Recipients of organ and tissue transplants require lifelong immunosuppression to prevent rejection. Better understanding of the processes culminating in allograft rejection has led to novel approaches to modulating the immune response. Co-stimulatory signals between antigen-presenting and -responding cells are essential for a normal alloimmune response, and blockade of these pathways during initial graft-host interaction may be used to ameliorate or prevent a destructive response from proceeding. A large number of experimental studies now support this concept, and early clinical trials have been initiated. Despite some early difficulties and many unanswered questions, co-stimulatory blockade has major potential as a future immune-modulating mechanism for use in clinical transplantation.

CD40 signaling and plaque instability

Today, multiple lines of evidence support the view of atherosclerosis as a chronic inflammatory disease and implicate components of the immune system in atherogenesis. Recent work has documented overexpression of the potent immune mediator CD40 and its counterpart CD40 ligand (CD40L) in experimental and human atherosclerotic lesions. Notably, interruption of CD40/CD40L interactions not only diminished the formation and progression of mouse atheroma, but also fostered changes in lesion biology and structure, which are associated in humans with "plaque stabilization." In accordance with the hypothesis that CD40 signaling promotes plaque instability, in vitro studies demonstrated that ligation of CD40 on atheroma-associated cell types, namely endothelial cells, smooth muscle cells, and macrophages, mediates functions considered crucial to the process of atherogenesis, such as the expression of cytokines, chemokines, growth factors, matrix metalloproteinases, and procoagulants. The combination of the broad gamut of proatherogenic biological responses triggered by ligation of CD40 on endothelial cells, smooth muscle cells, and macrophages in vitro and the results of in vivo studies of interruption of CD40 signaling suggests a central role for this receptor/ligand dyad during atherogenesis, proposing CD40/CD40L interactions as a novel potential therapeutic target for this prevalent human disease.

Recurrent autoimmune hepatitis after orthotopic liver transplantation

To determine the frequency, risk factors, and consequences of recurrent autoimmune hepatitis after liver transplantation, 41 patients with type 1 disease were monitored after surgery in accordance with a surveillance protocol. Tacrolimus or cyclosporine plus prednisone were administered to each patient, and liver biopsy examinations were performed at least annually according to protocol. Corticosteroid therapy was ultimately discontinued in only 2 patients. Recurrent disease was defined as the presence of lymphoplasmacytic infiltrates in liver tissue in the absence of other causes of allograft dysfunction. Autoimmune hepatitis recurred in 7 patients (17%), and the mean time to recurrence was 4.6 +/- 1 years. Recurrence was asymptomatic in 4 of 7 patients and detected only by surveillance liver biopsy assessment in 2 patients. Histological changes were mild, and there was no progression to cirrhosis during 4.9 +/- 0.9 years of observation. Five-year patient (86% v. 82%; P =.9) and graft (86% v. 67%; P =.5) survival rates were not statistically different between patients with and without recurrent disease. HLA-DR3 or HLA-DR4 occurred more commonly in patients with than without recurrence (100% v. 40%; P =.008) and healthy subjects (100% v. 49%; P =.01). Recurrent disease was unrelated to donor HLA status. In conclusion, recurrence after transplantation for type 1 autoimmune hepatitis is common. Its mild manifestations and favorable prognosis may reflect early detection by a surveillance protocol and/or continuous corticosteroid treatment. HLA-DR3- or HLA-DR4-positive recipients are at risk for recurrence regardless of donor HLA status.

Analysis of the CD40/CD40L role in the sustenance of alloreactive antibody production

CD40 ligand (CD40L) is important for T/B lymphocyte interaction. To understand the cellular basis of humoral allosensitization we, therefore: (1) measured CD40L protein and gene expression in sensitized and non-sensitized uremic unactivated peripheral CD4+ T lymphocytes; (2) studied the impact of blocking the CD40/CD40L pathway on alloreactive antibody (allo-Ab) production by engrafted sensitized PBLs into severe combined immunodeficient (SCID) mice after in vitro preactivation with IL2/LPs/HLA class II allopeptides and adjuvants as a potent stimulus to produce allo-Ab (Shoker et al. Transplantation 1999;68;1188); and (3) studied the modifying effect of CD40/CD40L blockade on T helper type I and II cytokine gene expression in the respective mice spleen. The CD40L protein was measured by flow cytometry and the gene expression was measured by quantitative RT-PCR. Alloreactive antibodies (alo-Abs) produced by sensitized PBLs engrafted into SCID mice with and without blockade of the CD40 receptor were measured by the PRA-STAT ELISA method. The modifying effects of CD40 blocking on allo-Ab production and cytokine gene expression by the engrafted cells measured by RT-PCR were then compared. There was no detectable CD40L protein expression in either the uremic or the control groups. The CD40L gene expression of 0.04 +/- 0.02 attomoles (aM) in the sensitized group was significantly higher than in the non-sensitized patients (0.009 +/- 0.007 aM, P < 0.0001) or the control CD4+ T cells (0.016 +/- 0.004 aM, P < 0.001). Blockade of the CD40 receptor abrogated the production of allo-Ab antibodies by the engrafted sensitized cells in 60% of the tested mice (n = 10); decreased the mean +/- S.D. optic density of allo-Ab to 0.1 +/- 0.13 and the mean +/- S.D. PRA to 12 + 16). In the presence of the control Ab, allo-Ab production in SCID sera was present in 100% of the 10 SCID mice tested; the mean +/- S.D. PRA was 75 +/- 20, and the mean + S.D. OD activity was 0.412 +/- 0.17. All cytokine genes were, otherwise, expressed in the presence or absence of CD40 blockade. The results suggest a potential role of an enhanced CD40/CD40L interaction in the sustenance of alloreactive antibody production without significant deviation to T helper-like I or II responses. Blocking the CD40/CD40L pathway may have a potential therapeutic benefit to treat sensitized uremic patients.

Kidney transplantation for end-stage renal failure in liver transplant recipients with hepatitis C viral infection

BACKGROUND

End-stage renal failure after successful liver transplantation (LTx) has been described in up to 5% of patients. Kidney transplantation (KTx) has been the treatment of choice in these cases. However, in recipients infected with hepatitis C virus (HCV), the augmentation of immunosuppression after KTx may result in an increased viral load. This, in turn, may adversely affect the liver allograft.

METHOD

The present study retrospectively examined the outcome in 17 patients (3 females and 14 males, mean age 51.1+/-11.3 years) who received KTx after LTx. The mean interval from LTx to KTx was 57.6+/-32.1 months. The mean follow-up was 41.7+/-20.5 months after KTx, and 99.6+/-37.7 months after LTx. Sixteen of the 17 patients received tacrolimus-based immunosuppression at the time of KTx.

RESULTS

During the follow-up period, one patient underwent combined liver and kidney retransplantation 3.7 years after KTx and 12.7 years after LTx. She subsequently died secondary to primary nonfunction. Four other patients died, two of lung cancer, one of pancreatitis/sepsis, and one of severe depression leading to noncompliance. A total of 29 episodes of biopsy-proven acute renal allograft rejection (1.7 episodes/ patient) were encountered and treated with steroids. Seven patients experienced a rise in liver function tests during the period of increased steroid dosage. Four patients received no treatment, and their liver function returned to baseline. The remaining three were treated with interferon. Overall 1- and 3-year actuarial patient and liver allograft survival was 88% and 71% (after renal transplantation); corresponding 1- and 3-year actuarial graft survival was 88% and 61%. Twelve patients are alive with normal liver function. One patient is on dialysis, because of renal allograft loss to noncompliance.

CONCLUSION

In this series, LTx recipients with HCV infection were able to undergo KTx with a reasonable degree of success. KTx should be offered for end-stage renal failure after LTx, even in the presence of HCV infection, to individuals with stable liver function and no signs of liver failure.

Knowledge about transplantation tolerance gained in primates

Research in transplantation tolerance relies on application of successful strategies in a nonhuman-primate organ transplant model for preclinical testing. Three principal approaches are being evaluated: hematopoietic chimerism, lymphocyte depletion and costimulation blockade. Interactive work in these three areas has yielded much new information on mechanisms of tolerance and opened the door to pilot clinical trials. Clinical application of xenotransplantation is likely to depend on such strategies.

Heightened CD40 ligand gene expression in peripheral CD4+ T cells from patients with kidney allograft rejection

BACKGROUND

CD40 ligand (CD40L) gene expression is increased in rejecting allograft biopsies. We, therefore, tested the possibility that CD40L gene expression is heightened in peripheral CD4+ T cells during renal allograft rejection.

METHODS

CD40L gene expression in peripheral blood CD4+ T cells from two renal transplant groups was measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR). Group 1: 20 patients with excellent renal transplant function; group 2: 25 patients with findings of acute and/or chronic allograft nephropathy (CAN); and group 3 of 12 normal controls. CD4+ cells were isolated by positive selection. The modifying effect of cyclosporine (CsA) and FK506 on CD40L gene expression was further tested in vitro in CD4+ T lymphocytes separated from pokeweed mitogen- (PWM) activated peripheral blood lymphocytes (PBL) preparations.

RESULTS

Mean+/-SD expressions of CD40L gene, in aM, in groups 1-3 were as follows: 0.0052+/-0.0094; 0.022+/-0.023 (P=0.0038 vs. group 2); and 0.014+/-0.005. Levels of CD40L gene expression correlated significantly with acute rejection Banff 97 score (R2=0.44, P=0.0004) and severity of intertubular capillary changes (ITCC) (R2=0.33, P=0.011). After in vitro activation, CD40L gene expression increased by approximately 4-fold and the addition of CsA or FK506 diminished CD40L gene expression to a base level.

CONCLUSION

Peripheral CD4+ T cell CD40L gene expression increases significantly in acute rejection and CAN and may serve as a non-invasive method to monitor allograft function and determine the biological response to CsA and FK506.

Inhibition of CD40 signaling limits evolution of established atherosclerosis in mice

Interruption of inflammatory pathways may provide a novel approach to the therapy of atherosclerosis. Recently, we and others have implicated the immune mediator dyad CD40/CD40L (CD40 ligand), which is expressed on endothelial and smooth muscle cells, macrophages, and T lymphocytes within human atherosclerotic lesions, in aspects of atherogenesis and the acute coronary syndromes, including regulation of matrix metalloproteinases, procoagulant activity, cytokines, etc. In vivo, interruption of CD40 signaling reduced the initiation and early phases of atheroma formation in hypercholesterolemic mice. However, whether interruption of CD40 signaling can retard the progression or even regress established lesions remains unknown. We report here that anti-CD40L antibody treatment of randomly assigned low-density lipoprotein receptor-deficient mice during the second half of a 26-week regimen of high-cholesterol diet did not regress, but did significantly reduce further evolution of established atherosclerotic lesions within the aortic arch and particularly the thoracic and abdominal aorta, as compared with control treatment (application of rat-IgG or saline; 13 weeks, continued high-cholesterol diet). In addition to limiting lesion progression, anti-CD40L treatment changed the composition of atheroma in manners thought to favor plaque stability, e.g., reduced relative content of macrophages and lipid, as well as increased relative content of smooth muscle cells and collagen. These data implicate CD40/CD40L as crucial mediators not only in the initial events of atherogenesis but also during the evolution of established atheroma. This study lends further support to the importance of this specific inflammatory signaling pathway in atherosclerosis and its complications.

Neoral use in the pediatric transplant recipient

This review and critical analysis of current trends of immunosuppression management in pediatric transplantation provides evidence and support for the continued role of Neoral as an indispensable part of immunosuppressive protocols. CyA formulation influences clinical outcomes such as acute rejection, as confirmed by two studies. The CyA microemulsion formulation provides more reliable and effective absorption. An advanced TDM strategy to determine CyA bioavailability can improve the effectiveness and safety of immunosuppression in de novo liver transplant patients. especially in the younger de novo patient. Neoral is an indispensable part of combination protocols in pediatric transplantation.

Neoral use in the cardiac transplant recipient

CyA is the core immunosuppressant of choice for the majority of transplant patients. The introduction of Neoral, a new microemulsion formulation of CyA. and more recently a range of adjunctive immunosuppressants have further enhanced the efficacy and tolerability of CyA-based immunosuppression. In the first year following transplantation the major causes of morbidity and death are graft failure, acute rejection, and systemic infection. Patients with deteriorated pulmonary circulation before transplantation are at increased risk of early postoperative death. Risk factors for early acute rejection include female donor sex, young donor age, and multiple HLA-DR mismatches. The principal cause of death in the long term is graft vasculopathy which accounted for 40% of all deaths. Risk factors that have been hypothesized to play a role in the pathogenesis of graft vasculopathy include hyperlipidemia, recipient age and gender, donor age, the number of HLA AB and DR mismatches, and CMV infection. Strategies proposed to reduce the risk of graft vasculopathy include aggressive use of lipid-lowering agents, avoidance of low CyA doses, and the use of adjunctive rapamycin or RAD therapy. Rejection surveillance therefore relies on routine serial endomyocardial biopsy. Recent research suggests that a more accurate assessment of the state of the graft can be obtained by considering the results across a number of biopsy samples obtained from different parts of the heart, rather than basing clinical judgment on the worst single result obtained. New molecular markers such as granzyme A mRNA are likely to improve the power of histology to diagnose and predict rejection. Neoral pharmacokinetics give greater bioavailability and less intrapatient variability than Sandimmune. In the keynote OLN 351 study comparing Neoral with Sandimmune in de novo heart transplant recipients, fewer Neoral patients needed antilymphocyte therapy to treat rejection, fewer female patients had rejection episodes in the Neoral group, the tolerability of the two formulations was equivalent, and there was a lower incidence of infections in the Neoral group. The clinical impact of Neoral in comparison with Sandimmune in de novo heart transplant patients has been investigated in a number of additional trials, including long-term studies, which have confirmed that Neoral is associated with: Lower CyA doses than Sandimmune. Equal or greater antirejection efficacy than Sandimmune. Comparable tolerability to Sandimmune. During the administration of intravenous CyA as an induction therapy in the days immediately following transplantation, there is evidence to suggest that a 6-hour infusion given twice daily, which mimics the pharmacokinetic profile of oral dosing, may be clinically more effective than a continuous 24-hour infusion. Milligram-for-milligram dose conversion from Sandimmune to Neoral is feasible. Following conversion, a reduction in the CyA dose may be required in the majority of patients to maintain target levels. In pediatric patients, the rate of elimination of CyA is greater and bioavailability increases with increasing age. Younger patients (less than 8 years of age) may be managed more effectively with a 3-times-daily, rather than a twice-daily dosing schedule. A number of studies have compared the clinical effects of Sandimmune and Neoral in maintenance therapy for cardiac transplant patients. As with de novo patients, these studies have found the new formulation of CyA to be associated with lower rates of acute rejection, lower therapeutic doses, and comparable tolerability. Milligram-to-milligram conversion from the old to the new CyA formulation is generally well tolerated, although in a minority of patients there is a significant increase in CyA levels. These may be associated with a transient increase in side effects which resolve on dose reduction. There is a dose-sparing effect with Neoral. Routine monitoring of both CyA and serum creatinine levels are adv

CD40 ligation induces tissue factor expression in human vascular smooth muscle cells

Tissue factor (TF) instigates the extrinsic pathway of blood coagulation. Plaque disruption and exposure of circulating factor VII/VIIa to subendothelial procoagulants such as TF leads to intravascular thrombosis, a frequent cause of acute atherosclerotic events. Although the expression of TF in the intima of human atherosclerotic lesions is well established, little is known about the mechanisms of TF regulation in vascular smooth muscle cells (SMC). We demonstrate here that TF colocalizes with the receptor CD40 on lesional SMC within atherosclerotic lesions in situ. In cultured vascular SMC, ligation of CD40 with native CD40 ligand (CD40L) derived from activated T lymphocytes or recombinant human CD40L (rCD40L) induced the transient expression of TF on the cell surface (as determined by FACS analysis) in a concentration- and time-dependent manner and enhanced total cell-associated TF (as determined by ELISA). CD40L-induced TF on vascular SMC is functional and activates coagulation. In accordance with the increased TF activity, stimulation of vascular SMC with rCD40L did not affect either protein expression or activity of tissue factor pathway inhibitors. In summary, these findings demonstrate the potential of the CD40/CD40L signaling pathway to augment the procoagulant activity in human vascular SMC. Because TF and CD40 colocalize on lesional SMC in human atheroma, CD40/CD40L signaling may contribute to the TF expression and hence to increased thrombogenicity of plaques during the inflammatory responses of atherogenesis and arterial injury.