Chronic graft rejection

Carbon Monoxide Suppresses Neointima Formation in Transplant Arteriosclerosis by Inhibiting Vascular Progenitor Cell Differentiation

[Figure: see text].

Combined abdominal heterotopic heart and aorta transplant model in mice

Background

Allograft vasculopathy (AV) remains a major obstacle to long-term allograft survival. While the mouse aortic transplantation model has been proven as a useful tool for study of the pathogenesis of AV, simultaneous transplantation of the aorta alongside the transplantation of another organ may reveal more clinically relevant mechanisms that contribute to the pathogenesis of chronic allograft rejection. Therefore, we developed a combined abdominal heart and aorta transplantation model in mice which benefits from reducing animal and drug utilization, while providing an improved model to study the progressive nature of AV.

Methods

The middle of the infrarenal aorta of the recipient mouse was ligatured between the renal artery and its bifurcation. Proximal and distal aortotomies were performed at this site above and below the ligature, respectively, for the subsequent anastomoses of the donor aorta and heart grafts to the recipient infrarenal aorta in an end-to-side fashion. The distal anastomotic site of the recipient infrarenal aorta was connected with the outlet of the donor aorta. Uniquely, the proximal anastomotic site on the recipient infrarenal aorta was shared to connect with both the inlet of the donor aorta and the inflow tract to the donor heart. The outflow tract from the donor heart was connected to the recipient inferior vena cava (IVC).

Results

The median times for harvesting the heart graft, aorta graft, recipient preparation and anastomosis were 11.5, 8.0, 9.0 and 40.5 min, respectively, resulting in a total median ischemic time of 70 min. The surgery survival rate was more than 96% (29/30). Both the syngeneic C57Bl/6 aorta and heart grafts survived more than 90 days in 29 C57Bl/6 recipients. Further, Balb/c to C57Bl/6 allografts treated with anti-CD40L and CTLA4.Ig survived more than 90 days with a 100% (3/3) survival rate. (3/3).

Conclusions

This model is presented as a new tool for researchers to investigate transplant immunology and assess immunosuppressive strategies. It is possible to share a common anastomotic stoma on the recipient abdominal aorta to reconstruct both the aorta graft entrance and heart graft inflow tract. This allows for the study of allogeneic effects on both the aorta and heart from the same animal in a single survival surgery.

Current progress in Reactive Oxygen Species (ROS)-Responsive materials for biomedical applications

Recently, significant progress has been made in developing “stimuli-sensitive” biomaterials as a new therapeutic approach to interact with dynamic physiological conditions. Reactive oxygen species (ROS) production has been implicated in important pathophysiological events, such as atherosclerosis,aging, and cancer. ROS are often overproduced locally in diseased cells and tissues, and they individually and synchronously contribute to many of the abnormalities associated with local pathogenesis. Therefore, the advantages of developing ROS-responsive materials extend beyond site-specific targeting of therapeutic delivery, and potentially include navigating,sensing, and repairing the cellular damages via programmed changes in material properties. Here we review the mechanism and development of biomaterials with ROS-induced solubility switch or degradation, as well as their performance and potential for future biomedical applications.

Ectonucleotidases in solid organ and allogeneic hematopoietic cell transplantation

Extracellular nucleotides are ubiquitous signalling molecules which modulate distinct physiological and pathological processes. Nucleotide concentrations in the extracellular space are strictly regulated by cell surface enzymes, called ectonucleotidases, which hydrolyze nucleotides to the respective nucleosides. Recent studies suggest that ectonucleotidases play a significant role in inflammation by adjusting the balance between ATP, a widely distributed proinflammatory danger signal, and the anti-inflammatory mediator adenosine. There is increasing evidence for a central role of adenosine in alloantigen-mediated diseases such as solid organ graft rejection and acute graft-versus-host disease (GvHD). Solid organ and hematopoietic cell transplantation are established treatment modalities for a broad spectrum of benign and malignant diseases. Immunological complications based on the recognition of nonself-antigens between donor and recipient like transplant rejection and GvHD are still major challenges which limit the long-term success of transplantation. Studies in the past two decades indicate that purinergic signalling influences the severity of alloimmune responses. This paper focuses on the impact of ectonucleotidases, in particular, NTPDase1/CD39 and ecto-5'-nucleotidase/CD73, on allograft rejection, acute GvHD, and graft-versus-leukemia effect, and on possible clinical implications for the modulation of purinergic signalling after transplantation.

Physiologically relevant oxidative degradation of oligo(proline) cross-linked polymeric scaffolds

Chronic inflammation-mediated oxidative stress is a common mechanism of implant rejection and failure. Therefore, polymer scaffolds that can degrade slowly in response to this environment may provide a viable platform for implant site-specific, sustained release of immunomodulatory agents over a long time period. In this work, proline oligomers of varying lengths (P(n)) were synthesized and exposed to oxidative environments, and their accelerated degradation under oxidative conditions was verified via high performance liquid chromatography and gel permeation chromatography. Next, diblock copolymers of poly(ethylene glycol) (PEG) and poly(ε-caprolactone) (PCL) were carboxylated to form 100 kDa terpolymers of 4%PEG-86%PCL-10%cPCL (cPCL = poly(carboxyl-ε-caprolactone); i% indicates molar ratio). The polymers were then cross-linked with biaminated PEG-P(n)-PEG chains, where P(n) indicates the length of the proline oligomer flanked by PEG chains. Salt-leaching of the polymeric matrices created scaffolds of macroporous and microporous architecture, as observed by scanning electron microscopy. The degradation of scaffolds was accelerated under oxidative conditions, as evidenced by mass loss and differential scanning calorimetry measurements. Immortalized murine bone-marrow-derived macrophages were then seeded on the scaffolds and activated through the addition of γ-interferon and lipopolysaccharide throughout the 9-day study period. This treatment promoted the release of H(2)O(2) by the macrophages and the degradation of proline-containing scaffolds compared to the control scaffolds. The accelerated degradation was evidenced by increased scaffold porosity, as visualized through scanning electron microscopy and X-ray microtomography imaging. The current study provides insight into the development of scaffolds that respond to oxidative environments through gradual degradation for the controlled release of therapeutics targeted to diseases that feature chronic inflammation and oxidative stress.

Mesenchymal Stem Cells in Combination with Scaffolds for Bone Tissue Engineering

This article reviews past and current strategies of the use of bone graft substitutes along with the future biologic alternatives that can enhance the functional capabilities of those grafts. Many of these bone graft substitute alternatives include ceramic-based, allograft-based, factor-based and polymer-based whereas others are cell-based. The ways of achieving the goal of tissue engineering using stem cells and their lineage to regenerate tissue have been detailed with regard to both the generation of sufficient vascular invasion of the tissue to improve oxygen and nutrient supply, and the development of innovative physical/chemical stimuli to induce bone formation with the proper biomaterial to carry the cells. It is imperative to integrate basic polymer science with molecular biology and stem cell biology, in the design of new materials that perform very sophisticated signaling needed for integration and function.

Prevention of intimal hyperplasia employing the cavitary two-layer method in allogeneic rat heart transplantation

BACKGROUND

The development of graft arteriosclerosis is a significant contributor to chronic rejection in organ transplant recipients. The purpose of the present study was to establish whether or not the cavitary two-layer method can prevent graft arteriosclerosis after rat heart transplantation.

METHODS

F-344 rats served as donors to Lewis recipients. Grafts in the control group (group C) were immediately allotransplanted without preservation. Grafts were also transplanted after cold preservation for 3 h in University of Wisconsin solution (group UW), or employing the cavitary two-layer (CTL) method (group TL). In another group (group W), grafts were subjected to 15-min warm ischemia and then transplanted. Grafts damaged by ischemia were also transplanted after preservation for 3 h using CTL (group WTL). We measured intimal thickening (IT) before transplantation and at 30 and 60 d post-transplant and also assessed the expression of heat shock proteins (HSPs).

RESULTS

At 60 d post-transplant, IT in group WTL was significantly lower than in group W (0.30 ± 0.03 versus 0.45 ± 0.04, respectively). In contrast, no significant changes were observed in the cold storage groups. Expression of HSPs 60 and 70 at 60 d in group WTL (25.40% ± 1.64% and 35.96% ± 2.65%, respectively) was reduced compared with group W (46.07% ± 5.84% and 55.11% ± 1.54%, respectively).

CONCLUSIONS

CTL reduces IT induced by warm ischemia in rat heart transplantation, and allows the maintenance of low HSP 60 and 70 expression.

Efficacy of mycophenolic acid combined with KRP-203, a novel immunomodulator, in a rat heart transplantation model

BACKGROUND

To explore a more effective and less toxic immunosuppressive strategy in organ transplantation, we recently developed the novel sphingosine-1-phosphate receptor agonist KRP-203. This study examined the efficacy of KRP-203 combined with mycophenolic acid (MPA), an active metabolite of mycophenolate mofetil, in rat heart allografts.

METHODS

Heterotopic heart transplantation was performed in a rat combination of DA (MHC haplotype: RT1(a)) to Lewis (RT1). The recipients were divided into 12 groups (n = 5-7): Syngeneic (Lewis to Lewis), Vehicle, KRP-203 (0.3 and 1 mg/kg), MPA (10 and 20 mg/kg), 10 mg/kg MPA with KRP-203 (0.03, 0.3, 1, and 3 mg/kg), and 20 mg/kg MPA with KRP-203 (0.3 and 1 mg/kg). MPA, KRP-203, and vehicle were given orally.

RESULTS

The mean days of survival were 5.8 (vehicle), 7 and 7.9 (0.3 and 1 mg/kg KRP-203, respectively), 12.7 and >54.4 (10 and 20 mg/kg MPA), >39.6 and >30.5 (10 mg/kg MPA with 1 and 3 mg/kg KRP-203), >100 and >87.8 (20 mg/kg MPA with 0.3 and 1 mg/kg KRP-203). Histologic and immunohistochemical analysis revealed that diffuse mononuclear cell infiltration (macrophages and T cells), hemorrhage, myocardial necrosis and fibrosis, and expression of endothelin-1, transforming growth factor-beta1, monocyte chemoattractant protein-1, interleukin-8, and E-selectin were markedly diminished in the allografts treated with MPA combined with KRP-203. Pharmacokinetic experiments indicated no interaction between MPA and KRP-203, and both combination regimens were well tolerated.

CONCLUSIONS

Combination therapy of MPA with KRP-203 has a therapeutic potential as a novel immunosuppressant strategy in clinical transplantation.

Correlation between endothelin expression in early post-transplant biopsy specimens and long-term allograft function in living-related renal transplantation

OBJECTIVE

We investigated whether degree of immunohistochemically evident endothelin (ET) expression in early post-transplant biopsy specimens could predict long-term allograft function in living-related renal transplantation.

METHODS

Allograft biopsy specimens obtained from 40 patients with living-related transplants were studied. Cases with episodes of acute rejection or calcineurin inhibitor toxicity were excluded. We immunostained graft biopsy specimens obtained at pre-transplantation (PRE) and at 3 months (3M) afterward with anti-ET antibody. The number of stained tubular epithelial cells per 1000 tubular cells was defined as the staining index (SI). In the 21 patients whom we could assess at 3 yr (3Y) after transplantation, the correlation between ET expression and long-term graft function was examined.

RESULTS

Anti-ET antibody staining was appreciable in tubular epithelium but not in glomeruli. Tubular SI at PRE and at 3M were 10.6 +/- 15.3 and 32.0 +/- 35.6 (mean +/- SD) respectively (p < 0.01). When patients were classified according to SI (group A, SI < 25; group B, SI > 25), declining ratio in creatinine clearance at 3Y after transplantation for groups A and B with respect was 21.8% +/- 15.4% and 41.9% +/- 21.6% (p < 0.05).

CONCLUSION

High ET expression in early post-transplantation, biopsy specimens was related to poor long-term allograft function following living-related renal transplantation.

A novel immunomodulator KRP-203 combined with cyclosporine prolonged graft survival and abrogated transplant vasculopathy in rat heart allografts

To find more effective and less toxic immunosuppressive strategies in long-term treatment for organ transplantation patients, we examined the effects on rat heart allograft survival of a novel sphigosine-1-phosphate receptor agonist, KRP-203, combined with a subtherapeutic dose of cyclosporine (CsA). Rat heart transplantation was performed across a major histocompatibility complex-incompatible (DA to LEW) rat combination. KRP-203 alone showed little or no effect on heart allograft survival. In contrast, KRP-203 combined with a subtherapeutic dose of CsA led to prolonged allograft survival. Histologic analyses showed that the combination completely suppressed acute rejection, as characterized by allograft vasculopathy, mononuclear cell infiltration, and myocardial necrosis in the heart allografts. RT-PCR analysis showed that the allografts treated with CsA or KRP-203 alone showed no suppression of IL-10, IFN-gamma, and TNF-alpha mRNA expression, but when combined with a subtherapeutic dose of CsA it completely suppressed their mRNA expressions. Furthermore, the combination treatment reduced donor-specific antibody production. KRP-203 combined with a subtherapeutic dose of CsA synergistically prolonged rat heart allograft survival. The combination of CsA with KRP-203 may provide an option to prevent allograft rejection and reduce adverse effects.

Analysis of Immune Markers in Human Cardiac Allograft Recipients and Association With Coronary Artery Vasculopathy

BACKGROUND

Because coronary artery vasculopathy (CAV) is a common cause of late cardiac allograft loss in humans, there is a need to develop and test non-invasive surrogate markers capable of detecting and predicting this disease entity.

METHODS

We performed a cross-sectional analysis of immune-based surrogate markers in 65 primary cardiac allograft recipients with or without angiographically documented CAV. Anti-donor cellular immunity was determined by interferon gamma (IFN)-gamma enzyme-linked immunosorbent spot (ELISPOT) assays using donor HLA-derived peptides (indirect pathway), and anti-donor alloantibodies were detected by flow cytometry using HLA-coated beads.

RESULTS

Anti-donor cellular and humoral immunity were detected more frequently in patients with CAV (17 of 32, 53.1%) than in controls (4 of 33, 12.1%) (p < 0.001). Anti-donor cellular and humoral immunity were detected in different sub-groups of CAV patients; peripheral blood lymphocytes (PBLs) from only 1 of 32 CAV patients reacted to donor peptides with simultaneous detection of peripheral anti-donor alloantibodies.

CONCLUSIONS

Immune reactivity in cardiac transplant recipients with CAV differs significantly from those without CAV and the detected responses are heterogeneous in nature. Serial assessments of anti-donor immunity using different methods will be required to detect and possibly predict outcome in cardiac transplant recipients.

Lymphoid neogenesis in chronic rejection: evidence for a local humoral alloimmune response

Recent advances indicate that, in various chronic inflammatory disorders, the activation of the immune system is triggered locally rather than in lymphoid organs. In this study, we have evaluated whether the humoral alloimmune response involved in chronic rejection is elicited within the graft. We used the rat aortic interposition model and microdissected the adventitia of the graft. Over time, the T cell infiltrate shifted toward a B helper phenotype. B lymphocyte clusters were detected and were the site of intense proliferation and apoptosis. Simultaneously, adventitial vascular endothelium acquired a high endothelial venule phenotype. Similar features were evidenced in the interstitium of chronically allografts (hearts and kidneys). Strikingly, ganocultured graft interstitial tissue was found to be the site of production of antibodies directed against donor MHC-I molecules. These findings, therefore, document the appearance of germinal centers in chronically rejected tissues. This lymphoid neogenesis implies that the graft is not only the target of the alloimmune response but also a site where this response actually develops, so as to optimize the communication between the targeted tissue and the immune effectors.

Heme oxygenase-1 (HO-1), a protective gene that prevents chronic graft dysfunction

Heme oxygenase-1 (HO-1) is a stress-responsive enzyme that acts during inflammatory reactions as the rate-limiting step in the catabolism of heme, yielding equimolar amounts of iron (Fe), biliverdin, and the gas carbon monoxide (CO). Expression of HO-1 regulates inflammatory and immune responses, such as those involved in the rejection of transplanted organs. We will discuss here accumulating evidence supporting the notion that expression of HO-1 in a transplanted organ can prevent its rejection. We will argue that the protective effects exerted by HO-1 are mediated to a large extent by the end products that it generates via the catabolism of heme. Better knowledge of how to enhance these protective effects is likely to help create new therapeutic strategies to improve the outcome of transplanted organs.

Mycophenolic acid inhibits platelet-derived growth factor-induced reactive oxygen species and mitogen-activated protein kinase activation in rat vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation is the major pathologic feature associated with chronic allograft nephropathy, and mycophenolic acid (MPA) inhibits VSMC proliferation. Since the role of inosine monophosphate dehydrogenase (IMPDH)-dependent de novo guanosine synthesis is limited in VSMCs, we examined the effects of MPA on platelet-derived growth factor (PDGF)-induced cellular ROS and mitogen-activated protein kinases (MAPK) activation in VSMCs. Primary cultured rat VSMCs were stimulated with PDGF-BB in the presence or absence of MPA. Cell proliferation was assessed by [3H]-thymidine incorporation, ROS by flow cytometry and MAPK activation by Western blot analysis. PDGF increased cell proliferation, cellular ROS and extracellular-regulated protein kinase (ERK) 1/2 and p38 MAPK activation by 3.4-, 1.6-, 3.3- and 3.9-fold, respectively. MPA at above 1 muM inhibited PDGF-induced cellular ROS and ERK 1/2 and p38 MAPK activation, as well as proliferation. Structurally different anti-oxidants and inhibitor of ERK or p38 MAPK blocked PDGF-induced proliferation. Anti-oxidants also inhibited ERK 1/2 and p38 MAPK activation. Exogenous guanosine partially recovered the inhibitory effect of MPA on VSMC proliferation. These results suggest that MPA may inhibit PDGF-induced VSMC proliferation partially through inhibiting cellular ROS, and subsequent ERK 1/2 and p38 MAPK activation in addition to inhibiting IMPDH.

Conversion from cyclosporine A to mycophenolate mofetil protects recipient kidney and prevents intimal hyperplasia in rat aortic allografts

BACKGROUND

Recent studies have demonstrated that complete conversion from cyclosporine A (CsA) to mycophenolate mofetil (MMF) prolongs graft survival in patients undergoing clinical organ transplantation. We investigated the effects of conversion from CsA to MMF on recipient kidneys and transplant arteriosclerosis in a rat aortic allograft model as a high responder combination.

METHODS

DA (MHC haplotype, RT1a) rat abdominal aortic grafts were orthotopically transplanted into Lewis (RT1l) rats. The recipients were divided into four oral treatment groups: (1) vehicle group, (2) CsA group (15 mg/kg/day), (3) CsA/MMF40 group (conversion from CsA 15 mg/kg/day to MMF 40 mg/kg/day on day 14), and (4) CsA/MMF20 group (conversion from CsA 15 mg/kg/day to MMF 20 mg/kg/day on day 14). On day 28 after transplantation, the rats were sacrificed and the hematoserological parameters were analyzed. The grafted aortas and recipient kidneys also were evaluated histologically and immunohistochemically.

RESULTS

The CsA group developed serological renal dysfunction, arteriolar hyalinosis, and apoptosis in the recipient kidneys, whereas the CsA/MMF40 and CsA/MMF20 groups did not. In the vehicle group, we observed remarkable intimal hyperplasia and marked inflammatory cell infiltration including macrophages and T cells. In the CsA group, intimal hyperplasia was evident without infiltration of macrophages or T cells. In the CsA/MMF40 and CsA/MMF20 groups, intimal hyperplasia was abrogated, while adventitial infiltration of and adhesion to the endothelium by macrophages and T cells occurred.

CONCLUSIONS

Conversion from CsA to MMF protected recipient kidneys and prevented transplant arteriosclerosis. However, insufficient immunosuppression by MMF might reactivate immune cells. This conversion therapy has preventive potential in transplant patients with CsA-associated nephrotoxicity and transplant arteriosclerosis.

Drug immunosuppression therapy for adult heart transplantation. Part 1: immune response to allograft and mechanism of action of immunosuppressants

In the early days of transplantation, immunosuppression therapy was rather broad and nonspecific, mainly using high-dose corticosteroids and azathioprine. Thereafter we progressively narrowed the target of immunosuppressive strategy starting with polyclonal antibodies. The introduction of cyclosporine, OKT3, and tacrolimus further narrowed the target on the T-cell pathways. More recently mycophenolate mofetil progressively took the place of azathioprine with its higher lymphocyte specificity and sirolimus and interleukin-2 receptor antibodies were introduced. In this field in constant movement the aim is to find a drug or a regimen that provides optimal immunosuppression therapy with minimal side effects, in other words to find the right balance between overimmunosuppression and underimmunosuppression therapy. This review is divided into two parts. The first part will provide a basic understanding of the immunologic response to allograft and explain how conventional and recently introduced immunosuppressive agents work. The second part will describe the clinical application of immunosuppressive drugs to provide practical information for those in charge of heart transplant recipients.

Oxidative stress in chronic renal allograft nephropathy in rats: effects of long-term treatment with carvedilol, BM 91.0228, or alpha-tocopherol

Oxidative stress is markedly increased after kidney transplantation and may participate in the development and/or progression of chronic renal allograft nephropathy. In the present study we sought to assess the nephroprotective potential of antioxidative treatment in renal allograft recipients. Experiments were performed in the Fisher-Lewis rat model of chronic renal allograft nephropathy, with isografted Lewis rats serving as controls. Allografted rats were orally treated with carvedilol, an antihypertensive drug with antioxidative properties (25 mg/kg/d), its purely antioxidative derivative BM 91.0228 (5 mg/kg/d), alpha-tocopherol (100 mg/kg/d), a combination of propranolol/doxazosine (10/5 mg/kg/d), or vehicle for 24 weeks. At the end of the study, oxidative status and influence of antioxidative treatment were assessed in transplanted animals. Chronic allograft nephropathy was characterized by a marked increase of markers for oxidative stress (increased plasma and kidney levels of malondialdehyde, reduced glutathione, and tocopherol levels in renal allografts). Treatment with carvedilol, BM 91.0228, and tocopherol significantly improved antioxidative status of allograft kidney recipients. In addition, carvedilol reduced elevated blood pressure in allografted rats. However none of the drugs had a beneficial influence on functional and morphologic renal changes. Our data thus demonstrate that long-term treatment with the antioxidants carvedilol, BM 91.0228, or alpha-tocopherol does not prevent development of chronic transplant nephropathy, despite an improvement of antioxidative status.

Everolimus for the prevention of allograft rejection and vasculopathy in cardiac-transplant recipients

BACKGROUND

Everolimus, a novel proliferation inhibitor and immunosuppressive agent, may suppress cardiac-allograft vasculopathy. We conducted a randomized, double-blind, clinical trial comparing everolimus with azathioprine in recipients of a first heart transplant.

METHODS

A total of 634 patients were randomly assigned to receive 1.5 mg of everolimus per day (209 patients), 3.0 mg of everolimus per day (211 patients), or 1.0 to 3.0 mg of azathioprine per kilogram of body weight per day (214 patients), in combination with cyclosporine, corticosteroids, and statins. The primary efficacy end point was a composite of death, graft loss or retransplantation, loss to follow-up, biopsy-proved acute rejection of grade 3A, or rejection with hemodynamic compromise.

RESULTS

At six months, the percentage of patients who had reached the primary efficacy end point was significantly smaller in the group given 3.0 mg of everolimus (27.0 percent, P<0.001) and the group given 1.5 mg of everolimus (36.4 percent, P=0.03) than in the azathioprine group (46.7 percent). Intravascular ultrasonography showed that the average increase in maximal intimal thickness 12 months after transplantation was significantly smaller in the two everolimus groups than in the azathioprine group. The incidence of vasculopathy was also significantly lower in the 1.5-mg group (35.7 percent, P=0.045) and the 3.0-mg group (30.4 percent, P=0.01) than in the azathioprine group (52.8 percent). The rates of cytomegalovirus infection were significantly lower in the 1.5-mg group (7.7 percent, P<0.001) and the 3.0-mg group (7.6 percent, P<0.001) than in the azathioprine group (21.5 percent). Rates of bacterial infection were significantly higher in the 3.0-mg group than in the azathioprine group. Serum creatinine levels were also significantly higher in the two everolimus groups than in the azathioprine group.

CONCLUSIONS

Everolimus was more efficacious than azathioprine in reducing the severity and incidence of cardiac-allograft vasculopathy, suggesting that everolimus therapy may alleviate this serious problem.

Regulatory cell-mediated tolerance does not protect against chronic rejection

BACKGROUND

Regulatory cells prevent graft loss to acute rejection and induce tolerance, possibly by promoting Th2 deviation. Th2 cytokines stimulate B cells, which cause alloantibody-mediated chronic rejection. We searched to determine whether regulatory cell-mediated tolerance protects or not against chronic rejection.

METHODS

Heart transplantation (Htx) was performed using RA (RT1P) and PVG (RT1c) rats as donor and recipients. Donor-specific blood transfusion (DSBT) was given on preTx day 12. Secondary grafts were implanted at day 100. Splenocytes were transferred from tolerant rats (and controls) into lightly irradiated (450 rad) naive PVG, which received RA Htx. Primary Htx were investigated for the development of vascular occlusion (VO), the production of Th1/Th2 intragraft cytokines, and for the nature of graft infiltrate as well as for endothelial deposition of immunoglobulin (Ig)G isotypes and complement (C3) binding. Results were compared with rejecting controls (no DSBT) and syngeneic Htx.

RESULTS

RA Htx were rejected within 10 days (8, 9, 10x4). PreTx DSBT prolonged primary Htx survival indefinitely (>140 days) with acceptance of secondary donor-specific (but not third-party) grafts (P<0.001). Naive irradiated PVG rats given splenocytes from tolerant rats but not from controls accepted RA Htx, showing the existence of regulatory cells in allograft acceptors. Despite being tolerant, DSBT-treated rats displayed typical features of chronic rejection at day 90 (VO=77%; P<0.001 vs. VO=4% in syngeneic rats). An overt Th2 deviation, particularly intragraft production of interleukin (IL)-4, was observed at day 30. Simultaneously to this Th2 deviation, B cells emerged in the grafts and endothelial deposition of IgG1 (Th2 dependent) and C3 binding were observed.

CONCLUSIONS

Regulatory cells that prevent graft loss to acute rejection in primary and secondary grafts do not protect against the development of chronic rejection.

Origin of vascular smooth muscle cells and the role of circulating stem cells in transplant arteriosclerosis

To date, clinical solid-organ transplantation has not achieved its goals as a long-term treatment for patients with end-stage organ failure. Development of so-called chronic transplant dysfunction (CTD) is now recognized as the predominant cause of allograft loss long term (after the first postoperative year) after transplantation. CTD has the remarkable histological feature that the luminal areas of intragraft arteries become obliterated, predominantly with vascular smooth muscle cells (VSMCs) intermingled with some inflammatory cells (transplant arteriosclerosis, or TA). The development of TA is a multifactorial process, and many risk factors have been identified. However, the precise pathogenetic mechanisms leading to TA are largely unknown and, as a result, adequate prevention and treatment protocols are still lacking. This review discusses the origin (donor versus recipient, bone marrow versus nonbone marrow) of the VSMCs in TA lesions. Poorly controlled influx and subsequent proliferative behavior of these VSMCs are considered to be critical elements in the development of TA. Available data show heterogeneity when analyzing the origin of neointimal VSMCs in various transplant models and species, indicating the existence of multiple sites of origin. Based on these findings, a model considering plasticity of VSMC origin in TA in relation to severity and extent of graft damage is proposed.

Targeting of macrophage activity by adenovirus-mediated intragraft overexpression of TNFRp55-Ig, IL-12p40, and vIL-10 ameliorates adenovirus-mediated chronic graft injury, whereas stimulation of macrophages by overexpression of IFN-gamma accelerates chronic graft injury in a rat renal allograft model

Adenovirus (Ad)-mediated gene transfer of immunoregulatory molecules prevents acute allograft rejection. It is here analyzed for the first time whether this approach may prevent the development of chronic renal allograft injury in rats. Renal allografts (F344-->Lewis rat) were ex vivo transduced in group I with control Ad-construct, group II with three different therapeutic Ad-constructs expressing the immunoregulatory molecules vIL-10, TNFRp55-Ig, and IL-12p40, and group III with AdIFN-gamma. Group IV served as untreated controls. Control grafts (IV) showed increasing proteinuria during the 24-wk follow-up. Chronic graft injury was accelerated by Ad-control (I) and even more by AdIFN-gamma (III). All rats carrying the AdIFN-gamma-transduced grafts died within 12 to 13 wk by advanced chronic renal failure associated with strong immune cell infiltration and immune gene expression. By contrast, the Ad-therapy group II showed less inflammation and improved graft histology and function if compared with the groups I and III. Moreover, significantly less infiltrating ED-1(+) macrophages and an improved histologic score even if compared with untreated controls (IV) was observed. However, after disappearance of therapeutic gene expression, group II showed increasing proteinuria probably as result of late T cell activation to the Ad-encoded proteins. Ex vivo transduction of allografts with Ad-control or even more AdIFN-gamma expression promotes intragraft inflammation and chronic graft injury. Targeting macrophage activation by a cocktail of therapeutic genes improved the results. These data support the pathogenetic role of cytokines in chronic graft injury; however, they also show the limitations of the Ad-mediated gene transfer.

Prevention of chronic rejection by pravastatin in a rat kidney transplant model

BACKGROUND

Pravastatin when administered with cyclosporine (CsA) has been shown to ameliorate transplant vasculopathy in the clinical setting. Previously we showed that pravastatin prevents chronic rejection in rat cardiac and liver transplant models. Here we determine whether pravastatin prevents chronic rejection in a rat renal allograft model.

METHODS

Orthotopic renal transplantations were performed using Fisher 344 rats as donors and Lewis rats as recipients. Recipients were treated with low-dose CsA for 10 days to prevent acute rejection. Recipients were divided into three groups: CsA, CsA + pravastatin, and syngeneic. Renal function was assessed by serum creatinine level at day 130. Allografts were evaluated by histology and immunohistochemistry. Serum levels of alloantibodies were measured by flow cytometry. Intragraft cytokine mRNA expression was determined by semiquantitative reverse transcriptase-polymerase chain reaction. Intragraft levels of the antiapoptotic Bag-1 gene were measured by Western blot.

RESULTS

Unlike allografts from the pravastatin group, control allografts demonstrated glomerulosclerosis, vascular obliteration, tubular atrophy, and interstitial fibrosis. Serum creatinine levels and graft infiltration of T cells and macrophages in the pravastatin-treated animals were significantly lower. Intragraft cytokines showed a T helper 2 polarization and decreased transforming growth factor-beta in the pravastatin group. Intragraft expression of Bag-1 was increased in the pravastatin group.

CONCLUSION

This study demonstrates the ability of pravastatin to inhibit chronic rejection in rat renal allografts. Pravastatin's pleiotropic effects of reducing intragraft inflammatory cytokines, inhibiting immune cell infiltration, and causing up-regulation of the antiapoptotic gene Bag-1 suggest that its ability to prevent transplant chronic rejection may be multifactorial.

Genetic polymorphisms influencing therapy and susceptibility to rejection in organ allograft recipients

Solid organ transplantation during the past 30 years has developed from an experimental procedure into routine clinical practice. The current repertoire of immunosuppressive agents has made a major contribution to transplant survival; however, problems in different areas still need to be overcome. Several gene polymorphisms are supposed to influence immunosuppressive therapy and susceptibility to rejection. Therefore, a priority of transplant biologists is to estimate individual patient risk and to characterise the genetic profile of patients in need of a transplant in order to optimise the use of a scarce resource such as organs from cadaver donors, and to avoid serious drug-induced adverse effects. Polymorphisms in genes encoding tumour necrosis factor-alpha (TNFalpha), interleukin (IL)-6, IL-10, interferon-gamma (IFNgamma), transforming growth factor-beta (TGFbeta) and thiopurine S-methyltransferase (TPMT) can have significant effects on an individual's risk of rejection, as well as their ability to tolerate immunosuppressive therapy. Genotyping of known polymorphisms in these genes may in the future contribute to our ability to individualise immunosuppressive therapy in organ transplant recipients.

Ligation of HLA class I molecules on endothelial cells induces phosphorylation of Src, paxillin, and focal adhesion kinase in an actin-dependent manner

The development of chronic rejection is the major limitation to long-term allograft survival. HLA class I Ags have been implicated to play a role in this process because ligation of class I molecules by anti-HLA Abs stimulates smooth muscle cell and endothelial cell proliferation. In this study, we show that ligation of HLA class I molecules on the surface of human aortic endothelial cells stimulates phosphorylation of Src, focal adhesion kinase, and paxillin. Signaling through class I stimulated Src phosphorylation and mediated fibroblast growth factor receptor (FGFR) translocation to the nucleus. In contrast, Src kinase activity was not involved in class I-mediated transfer of FGFR from cytoplasmic stores to the cell surface. Inhibition of Src protein kinase activity blocked HLA class I-stimulated tyrosine phosphorylation of paxillin and focal adhesion kinase. Furthermore, HLA class I-mediated phosphorylation of the focal adhesion proteins and FGFR expression was inhibited by cytochalasin D and latrunculin A, suggesting a role for the actin cytoskeleton in the signaling process. These findings indicate that anti-HLA Abs have the capacity to transduce activation signals in endothelial cells that may promote the development of chronic rejection.

Persistent rejection of peritubular capillaries and tubules is associated with progressive interstitial fibrosis

BACKGROUND

We have reported that a 12-day course of high dose cyclosporine A treatment in thymectomized miniature swine with major histocompatibility complex (MHC) class I-mismatched renal allografts results in transient acute rejection followed by either in chronic rejection (progression group) or graft acceptance (recovery group). Here, we examined the differential features between both groups in the peritubular capillaries (PTCs) and tubules to clarify the pathogenesis of the progressive interstitial fibrosis in chronic rejection.

METHODS

Morphometric and immunohistochemical studies were performed on serial renal biopsies (days 0 to 100) obtained from both groups, focusing on the cellular infiltrate, rejection of PTCs and tubules, myofibroblast accumulation, and progressive interstitial fibrosis.

RESULTS

In the progression group, acute rejection occurred by day 8 and progressed to chronic rejection by day 100, with the development of interstitial fibrosis. PTC endothelial cell and tubular epithelial cell death associated with CD3+ cell infiltration was evident, confirmed by nick end-labeling (TUNEL), commencing by day 8 and continuing thereafter. In acute rejection, destruction of PTCs and tubules accompanied by disruption of basement membrane (BM) occurred with capillaritis or tubulitis in areas with a severe cellular infiltrate. During the development of chronic rejection, capillaritis of PTCs and tubulitis continued by day 100, accompanied by persistent T cell infiltration, and the remaining PTCs and tubules exhibited progressive atrophy with thickening and/or lamination of BM. On day 100, identifiable PTCs and tubules were lost in areas of interstitial fibrosis. Proliferating (PCNA+) alpha-actin+ myofibroblasts accumulated around PTCs, tubules and in interstitium, and widespread interstitial fibrosis developed by day 100. In contrast, in the recovery group, injured PTCs and tubules recovered by day 100 based on the resolution of acute rejection, and minimal loss of PTCs and tubules was evident by day 100 with minimal interstitial fibrosis.

CONCLUSIONS

Persistent rejection directed at PTCs and tubules, and proliferation of myofibroblasts are prominent features in the progressive interstitial fibrosis in chronic rejection, and are probably key events in its pathogenesis.

Treatment of chronic renal allograft rejection in rats with a low-molecular-weight heparin (reviparin)

BACKGROUND

Low-molecular-weight heparin (LMWH) has been shown to prolong survival of rat cardiac allografts independently from immunosuppressive treatment. Furthermore, long-term treatment reduces the development of chronic graft vascular disease after experimental heart transplantation. The aim of the present study was to determine whether treatment with the LMWH reviparin has a beneficial effect on chronic rejection in a rat renal allograft model.

METHODS

Kidneys of Fisher (F344) rats were transplanted into unilaterally nephrectomized Lewis (LEW) recipients. LEW-->LEW isografts served as controls. Animals were treated with cyclosporine (5 mg/kg/d) for the first 10 days. Nephrectomy of the remaining kidney was performed after 10 days. Allografted animals were treated either with reviparin (2 mg/kg/d subcutaneously) for 24 weeks (Allo-24), from week 12 to 24 (Allo-12), or with vehicle for 24 weeks. Proteinuria was determined at regular intervals. Kidneys were harvested after 24 weeks for histomorphological and immunohistochemical evaluation.

RESULTS

No major bleeding complications were observed in reviparin-treated animals. Proteinuria was significantly reduced in allografted animals both by early as well as by late-onset treatment with reviparin. Transplant glomerulopathy was diminished in Allo-24 and in Allo-12 groups compared to vehicle-treated animals, whereas tubulointerstitial inflammation was influenced only in animals immediately treated with reviparin. Immunohistochemical studies demonstrated a marked reduction of renal monocyte and T-cell infiltration as well as expression of MHC II by treatment with reviparin.

CONCLUSIONS

Treatment with the LMWH reviparin significantly improved chronic renal allograft rejection in the F344-to-LEW rat model, both after early and late start of therapy. Although the exact mechanisms of this beneficial effect remain unclear, our data offer a potential new therapeutical approach for prevention of chronic allograft nephropathy.

L-arginine polymer mediated inhibition of graft coronary artery disease after cardiac transplantation

BACKGROUND

Nitric oxide (NO) limits the development of graft coronary artery disease (GCAD) in transplanted hearts. We hypothesized that l-arginine polymers administered to cardiac allografts ex vivo would translocate across vascular cellular membranes, up-regulate inducible nitric oxide synthase (iNOS) production of NO, and inhibit the development of GCAD.

METHODS

Three groups of PVG rat donor hearts were incubated with either 0.8 ml phosphate-buffered saline, (PBS, n=12) or 50 microM L-arginine polymer solutions of length five (R5, n=12) or nine (R9, n=12) prior to heterotopic transplantation into ACI recipients. Graft vessels were scored at POD 60 and 90 for percentage luminal narrowing (%LN), intima to media ratio (I/M), and percentage affected vessels (%AV). Translocation efficiency was determined by treatment with biotinylated polymers. NO production of treated aortic segments was determined in vitro by Griess reaction.

RESULTS

Translocation efficiencies were 89+/-19% (R9), 7+/-10% (R5), and 0+/-0% PBS (ANOVA, P<0.001) which corresponded to NO production in treated aortic segments of 0.175+/-0.17 (R9), 0.120+/-0.006 (R5), and 0.135+/-0.035 microM/mg (PBS), (ANOVA, P=0.002). GCAD scores at POD 60 were: %LN: 3.2+/-3.8% (R9), 12.6+/-6.7% (R5), 11.3+/-4.2% (PBS) (ANOVA, P=0.025); I/M: 0.03+/-0.04 (R9), 0.13+/-0.07 (R5), 0.12+/-0.05 (PBS) (ANOVA, P=0.037); %AV: 7+/-7% (R9), 19+/-7%(R5), 22+/-9%(PBS) (ANOVA, P=0.021). Reduction of GCAD parameters was maintained at POD 90.

CONCLUSION

R9 efficiently translocated across cytoplasmic membranes, enhanced vascular NO production, and decreased neointimal hyperplasia. This ex vivo treatment may have a therapeutic role in preventing GCAD.

Origin of neointimal endothelium and alpha-actin-positive smooth muscle cells in transplant arteriosclerosis

The development of transplant arteriosclerosis (TA) is today's most important problem in clinical organ transplantation. Histologically, TA is characterized by perivascular inflammation and progressive intimal thickening. Current thought on this process of vascular remodeling assumes that neointimal vascular smooth muscle (VSM) cells and endothelium in TA are graft-derived, holding that medial VSM cells proliferate and migrate into the subendothelial space in response to signals from inflammatory cells and damaged graft endothelium. Using MHC class I haplotype-specific immunohistochemical staining and single-cell PCR analyses, we show that the neointimal alpha-actin-positive VSM cells in rat aortic or cardiac allografts are of recipient and not of donor origin. In aortic but not in cardiac allografts, recipient-derived endothelial cells (ECs) replaced donor endothelium. Cyclosporine treatment prevents neointima formation and preserves the vascular media in aortic allografts. Recipient-derived ECs do not replace graft endothelium after cyclosporine treatment. We propose that, although it progresses beyond the needs of functional repair, TA reflects the activity of a normal healing process that restores vascular wall function following allograft-induced immunological injury.

The transforming growth factor-beta1 codon 10 gene polymorphism and accelerated graft vascular disease after clinical heart transplantation

BACKGROUND

The multifunctional cytokine transforming growth factor- (TGF) beta1 is thought to play a role in the pathogenesis of graft vascular disease (GVD). Polymorphisms at codon 10, (Leu10-->Pro) and codon 25 (Arg25-->Pro) in the signal sequence of the TGF-beta1 gene regulate the production and secretion of the protein. We investigated whether these polymorphisms are risk factors for the development of GVD after clinical heart transplantation.

METHOD

TGF-beta1 polymorphisms, Leu10-->Pro and Arg25-->Pro, were determined in DNA from heart transplant recipients (n=252) and their donors (n=213), using sequence-specific oligonucleotide probing. GVD was angiographically diagnosed 1 year after transplantation. In addition other potential risk factors including underlying disease, recipient and donor age, recipient and donor gender, number of acute rejections in the first year, cold ischemia time, and HLA mismatches were analyzed by univariate and multivariate logistic regression analysis.

RESULTS

Univariate analysis showed that the recipient TGF-beta1 polymorphism Leu10-->Pro, (P=0.056, chi2 test), underlying disease (P=0.01, chi2 test), number of acute rejections in the first-year (P=0.03, analysis of variance), and donor age (P<0.001, analysis of variance) were risk factors for the development of GVD. The TGF-beta1 Arg25-->Pro polymorphism was not a risk factor. Also in the multivariate analysis, the recipient TGF-beta1 codon 10 polymorphism was associated with GVD, with patients homozygous for Pro at greatest risk (odds ratio 7.7, P=0.03). Apart for the recipient TGF-beta1 Leu10-->Pro polymorphism, donor age appeared to be an independent risk factor for the development of GVD at 1 year. Patients with older donor hearts were at greater risk than patients receiving grafts from younger donors (odds ratio 1.1/year, P<0.001).

CONCLUSION

Recipient TGF-beta1 Leu10-->Pro polymorphism and higher donor age are independent risk factors for the development of GVD after clinical heart transplantation.

RAD in de novo renal transplantation: comparison of three doses on the incidence and severity of acute rejection

BACKGROUND

The effects of three doses of RAD (40-O-[2-hydroxyethyl]-rapamycin), a novel macrolide with potent immunosuppressive and antiproliferative properties, on the incidence and severity of acute rejection episodes as well as its tolerability were evaluated in a dose-ranging study in de novo renal transplant recipients.

METHODS

In this double-blind, parallel group, multicenter study, recipients were randomized to receive 1 mg, 2 mg, or 4 mg/day of RAD in combination with Neoral (cyclosporine, USP MODIFIED) and corticosteroids. The incidence and severity of biopsy-proven acute rejection episodes, graft survival, patient survival, infection rates, laboratory measurements, and adverse events were compared across groups after 6 months of therapy.

RESULTS

Among the 103 recipients, patients receiving 1, 2, or 4 mg/day experienced a 32.4%, 14.7%, or 25.7% incidence of biopsy-proven acute rejection episodes within the first 6 months posttransplantation, respectively. Even though the study was not powered to demonstrate efficacy, the incidence of moderate and severe acute rejection episodes was found to be significantly lower among patients in the 2 mg and 4 mg/day groups than in the 1 mg/day group (P=0.002 and P=0.006, respectively). Overall graft and patient survival rates were excellent. RAD was generally well tolerated. Although blood lipid levels increased in all groups, changes were manageable with lipid-lowering agents and did not warrant discontinuation of study medication. The incidence of viral and fungal infections was low; however, it was higher among recipients treated with 4 mg/day.

CONCLUSIONS

In combination with Neoral and corticosteroids, RAD doses of 2 mg and 4 mg/day resulted in lower rates of acute rejection episodes and efficacy failure than the 1 mg/day dose and were significantly more effective in reducing the severity of rejection. Large-scale, controlled, follow-up studies are currently in progress to confirm these initial findings.

INTRATHYMIC IMMUNE MODULATION PREVENTS ACUTE REJECTION BUT NOT THE DEVELOPMENT OF GRAFT ARTERIOSCLEROSIS (CHRONIC REJECTION)1

BACKGROUND

We showed previously that our intrathymic immune modulation protocol induces virtually permanent graft survival of simultaneously transplanted cardiac allografts in MHC-incompatible rat strain combinations. It is, however, unknown whether this procedure prevents the development of graft arterial disease (GAD).

METHODS

Male AO recipient rats were intrathymically inoculated with 2.5x10(7) PVG splenocytes immediately followed by heterotopic transplantation of a PVG cardiac allograft (day 0). Immunosuppression consisted of 1 ml of antilymphocyte serum i.p. (day 0) and cyclosporine i.m. (15 mg/kg body weight) on days 1, 2, and 3 posttransplantation. Histological analysis, mixed lymphocyte reactions, and intragraft cytokine mRNA expression were performed at several time points after engraftment.

RESULTS

Histological analysis revealed that GAD was already present 14 days after transplantation. At 200 days, virtually all vessels were affected and over 80% of the vessels showed severe intimal lesions. Infiltrate analysis displayed massive parenchymatous infiltrates (CD8+ cells and ED1+ macrophages) 2 weeks after transplantation. At later time points, infiltrates became epicardial and/or blood vessel associated and mainly consisted of CD4+, CD8+, and B cells. Mixed lymphocyte reactions showed nonspecifically decreased responses at 60 days but complete restoration of these responses at later time points (120 to 280 days). Intragraft cytokine mRNA expression showed decreased interleukin-2/interferon-gamma and sustained interleukin-10 expression 2 weeks after transplantation. Transforming growth factor-beta mRNA expression was increased >200 days after transplantation.

CONCLUSIONS

Intrathymic immune modulation does not abolish alloreactivity, and despite induction of long-lasting graft survival, this procedure does not prevent and may even facilitate the development of GAD.

Recipient origin of neointimal vascular smooth muscle cells in cardiac allografts with transplant arteriosclerosis

BACKGROUND

Coronary artery disease is today's most important post-heart transplantation problem after the first perioperative year. Histologically, coronary artery disease is characterized by transplant arteriosclerosis. The current view on this vasculopathy is that vascular smooth muscle (VSM) cells from the media of affected arteries proliferate and migrate into the sub-endothelial space (intima) in response to signals from inflammatory cells and damaged graft endothelium. According to this model, the intimal VSM cells in transplant arteriosclerotic lesions should originate from donor tissue. Using recipient-specific polymerase chain reaction (PCR) analysis of microdissected, single, neointimal VSM nuclei, we recently showed that after allogeneic aorta transplantation the neointimal VSM cells are of recipient and not of donor origin. In this study, we analyzed whether VSM-cell replacement with recipient-derived cells also takes place after allogeneic heart transplantation.

METHODS

Cardiac allografts, when transplanted from female donors to male immune-modulated recipient rats, eventually developed transplant arteriosclerosis. We microdissected alpha-actin positive neointimal VSM cells from tissue sections and determined the origin (donor or recipient) using recipient-specific (male), single-cell, PCR analysis.

RESULTS

In total, we analyzed 35 VSM-cell nuclei from 3 allografts, and PCR analysis revealed that 30/35 (86%) of the samples displayed the male-specific 128 base pair DNA fragment. These results indicate that after allogeneic cardiac transplantation, at least 86% of VSM cells in transplant arteriosclerotic lesions are of recipient origin.

CONCLUSIONS

In contrast to current thought, the neointimal VSM cells in cardiac allografts that show transplant arteriosclerosis are of recipient and not of donor origin.

The role of the graft endothelium in transplant rejection: evidence that endothelial activation may serve as a clinical marker for the development of chronic rejection

In this review, we discuss the role of the allograft endothelium in the recruitment and activation of leukocytes during acute and chronic rejection. We discuss associations among endothelial activation responses, the expression of adhesion molecules, chemokines and chemokine receptors, and rejection; and we propose that endothelial vascular cellular adhesion molecule-1 (VCAM-1) may be used as a surrogate marker of acute rejection and allograft vasculopathy. In addition, we describe potential mechanistic interpretations of persistent endothelial cell (EC) expression of major histocompatibility complex (MHC) class II molecules in allorecognition. The graft endothelium may provide an antigen-specific signal to transmigrating, previously activated, T cells and may induce B7 expression on locally transmigrating leukocytes to promote costimulation. Taken together, these functions of the EC provide it with a potent regulatory role in rejection and in the maintenance of T-cell activation via the direct and/or the indirect pathways of allorecognition.

Alloreactive cytotoxic CD4+ responses elicited by cytomegalovirus-infected endothelial cells: role of MHC class I antigens

Cytomegalovirus (CMV) has been associated with chronic graft rejection in solid organ transplant patients. To elucidate the mechanism by which CMV leads to graft rejection, we hypothesized that CMV infection of endothelial cells could stimulate alloreactive cytotoxic T lymphocytes (CTL). This hypothesis was explored using the following experimental model: peripheral blood mononuclear cells (MNC) obtained from normal hosts were grown on monolayers of umbilical vein endothelial cells (UVEC) infected with CMV (CMV-UVEC) or not (control) and tested for CTL activity against uninfected UVEC. We showed that CMV-UVEC-stimulated MNC have significant CTL activity against uninfected UVEC. The CTL activity elicited by CMV-UVEC stimulation was significantly higher compared with that stimulated by uninfected UVEC or by ganciclovir-treated CMV-UVEC, indicating the critical role of productive CMV infection. The CTL activity was specific for the UVEC used as stimulators and did not affect MHC-unrelated UVEC. However, lymphoblastoid lines (LBL) major histocompatibility complex (MHC)-identical with the stimulator UVEC were also killed by the CMV-UVEC-stimulated MNC. CTL killed identical UVEC and LBL in a competitive fashion. Blocking experiments with monoclonal antibodies (mAbs) identified CD4 cells as the main effector of CTL activity and MHC class I as the antigenic target of CTL. Although natural killer (NK) cells did not significantly contribute to the CTL activity of CMV-UVEC-stimulated MNC, their presence in the MNC cultures during the stimulation process was critical for the development of CTL. This model offers a framework for understanding the role of CMV infection in graft rejection and for devising preventative strategies.

Activation of NF-kappa B in human endothelial cells induced by monoclonal and allospecific HLA antibodies

Chronic graft rejection, characterized by a gradual occlusion of grafted vessels, is the most serious complication following heart and kidney transplantation. Although often associated with chronic production of anti-HLA and anti-endothelial antibodies, the precise role of antibodies in chronic rejection remains uncertain. Here we have investigated whether HLA-specific antibodies, either monoclonal or derived from patients, cause endothelial cell activation. Thus we investigated tyrosine phosphorlyation, NF-kappaB activation and cell proliferation in human umbilical vein endothelial cells (HUVEC) or microvascular endothelial cells from adult human heart (CMEC). Ligation of monomorphic determinants of MHC class I molecules (using the mAb W6/32) on the surface of HUVEC caused an increase in tyrosine phosphorylation of proteins of mol. wt approximately 75-80 kDa. Similarly, ligation of monomorphic determinants on both CMEC and HUVEC resulted in increased NF-kappaB binding compared to controls (by 74.4 and 52.5%, P = 0.001) and this was enhanced by addition of secondary antibody. Two HLA-specific mAb resulted in a 277 and 170% increase in NF-kappaB-binding activity compared to controls. Four patient samples containing HLA antibodies were used against HLA-specific HUVEC and four samples were incubated with HUVEC bearing irrelevant antigens. Patient sera alone enhanced NF-kappaB binding by 27-186%, but only when added to HUVEC bearing relevant antigens. W6/32 and allospecific antibodies from patients significantly enhanced HUVEC proliferation, measured by uptake of [(3)H]thymidine. In conclusion, activation of NF-kappaB by human anti-HLA antibodies demonstrates their potential role in pathogenesis of chronic vascular occlusive disease following transplantation.

ICAM-1 affects reperfusion injury and graft function after cardiac transplantation

BACKGROUND

The effects of increased expression of intercellular adhesion molecule (ICAM-1), an important mediator of neutrophil-mediated reperfusion injury (RI), were assessed in donor cardiac allografts in a heterotopic rat transplantation model.

METHODS

At -24 h, PVG donors were untreated (n = 35) or treated (n = 37) with lipopolysaccharide (LPS, 5 mg/kg ip). Hearts were procured at 0 h, stored at 4 degrees C for 45 min, and grafted heterotopically into ACI recipients pretreated with vehicle or anti-ICAM-1 (1A29) mAb. Intracardiac balloons (n = 8 per group) were used to measure allograft left ventricular function (dP/dt) prior to harvest and following reperfusion. RI was assessed at 6, 12, and 24 h by myeloperoxidase (MPO) levels, percentage wet weight (%w/w), and percentage contraction band necrosis (%CBN).

RESULTS

At 12 h, LPS-pretreated grafts showed increased ICAM-1 expression by Northern blot (n = 3) and immunohistochemistry (n = 3) and significantly increased MPO (0.33 +/- 0.2 U/mg vs 0.05 +/- 0.04 U/mg at 12 h), %w/w (81.7 +/- 1.8% vs 79.2 +/- 0.7% at 12 h), and %CBN (15.2 +/- 1. 9% vs 11.4 +/- 2.0% at 24 h). LPS pretreatment had no effect on graft function at early time points (baseline to 2 h) but led to depressed dP/dt at later time points with trends toward significance at 12 h (2101 +/- 1653 mmHg/s vs 173 +/- 201 mmHg/s, P = 0.06, ANOVA). Recipient 1A29 treatment (n = 6 per group) reversed the effects of LPS pretreatment in all three RI parameters and significantly improved functional recovery.

CONCLUSIONS

Alteration of cardiac graft phenotype to that likely seen in clinical organ donors leads to increased delayed-onset myocardial RI following transplantation in this model. The blockade of this increased RI following 1A29 mAb treatment supports a central role for ICAM-1 in this process.

Orthotopic aortic transplantation in mice: a new model of allograft arteriosclerosis

BACKGROUND

Graft arteriosclerosis is a major cause of death after allotransplantation of organs such as the heart or the kidney. Aortic allotransplantation in mice is a useful experimental model to study the mechanisms of this pathology. However, the conventional heterotopic aortic model is limited by a high morbidity and is technically difficult to perform. We developed a new simple method for aortic transplantation in mice.

METHODS

The infrarenal aorta from the donor mouse was anastomosed to the recipient's aorta at the same position using a sleeve technique. Orthotopic aortic transplantation was performed in 45 mice, 5 isografts and 40 allografts. No immunosuppression was given, and the mice were killed at day 15 or 30. The graft was examined macroscopically, and several histologic sections were made.

RESULTS

The overall survival rate was 78%. The incidence of thrombosis was low (4 cases) compared with previously published series. Histology of aortas revealed typical aspects of rejection in the allografts with a chronic picture at day 30. No significant lesion was observed in isografts.

CONCLUSIONS

We have developed a model of orthotopic aortic transplantation in mice. This new model is easy to carry out and has a low incidence of thrombosis, probably because there is no size discrepancy between donor and recipient aortic segment.

Chronic allograft rejection. Do the Th2 cells preferentially induced by indirect alloantigen recognition play a dominant role?

Chronic rejection has been the major obstacle to the long-term allograft survival in the clinic. Although the etiology of this rejection reaction is multifactorial, alloantigen-specific immune activation plays the most critical role. We herein hypothesize that CD4+ Th2 cells that are preferentially induced by the indirect recognition of allogeneic histocompatibility antigens late in transplantation may play the most critical role in the initiation and/or maintenance of chronic allograft rejection. Immunosuppression used to prevent acute rejection and the nature of antigen-presenting cells and alloligands in the graft may all contribute to immune deviation to the Th2 response. This response may be further perpetuated by type 2 cytokines conceivably produced by activated macrophages, NK cells, and CD8+ T cells in the graft. Cytokines and growth factors induced by this type 2 response, in turn, allow for activation of B, endothelial, and smooth muscle cells that collectively contribute to the pathogenesis of chronic allograft rejection by producing alloantibodies and growth hormones required for interstitial fibrosis, extracellular matrix deposition, and vascular neointimal hyperplasia.

Prevention of chronic renal allograft rejection in rats with an oral endothelin A receptor antagonist

BACKGROUND

Chronic rejection is the most common cause of graft loss in renal transplantation. The pathomechanisms underlying chronic rejection are poorly understood, and no treatment has yet successfully been established. We hypothesized that, in analogy to models of reduced renal mass, the administration of a selective endothelin (ET) A receptor antagonist could improve the course of chronic rejection in renal allografts.

METHODS

Experiments were performed in the Fisher-to-Lewis rat model of chronic rejection. Lewis-->Lewis isografts served as controls. Animals were treated with either the oral selective ET-A receptor antagonist LU135252 (50 mg/kg/day) or vehicle. Animal survival, blood pressure, creatinine clearance, proteinuria, and urinary ET excretion were investigated for 24 weeks. Kidneys were removed for light microscopical evaluation, determination of ET mRNA expression and tissue protein concentration, and immunohistochemical assessment of cell surface markers.

RESULTS

Rats with chronic rejection showed an increase in renal ET mRNA synthesis and ET protein content. Treatment with LU135252 resulted in a significant improvement in survival after 24 weeks (0.92 vs. 0.38, P<0.01 by log-rank test). Creatinine clearance was higher in animals treated with the selective ET-A receptor antagonist (P<0.05). LU135252 had no influence on blood pressure and proteinuria. Selective ET-A blockade was associated with significantly less morphological changes and a significant reduction of expression of cell surface markers for macrophages (ED1), T cells (R73), and MHC II (F17-23-2).

CONCLUSION

The renal ET-A system plays an important role in the pathomechanisms underlying chronic renal allograft rejection, because the treatment with a selective ET-A receptor antagonist dramatically improves the course of chronic renal failure after allograft transplantation. These results offer a novel therapeutical option for treatment of chronic renal allograft rejection, for which so far no therapy is known.

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

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