Alloimmunity and nonimmunologic risk factors in cardiac allograft vasculopathy

G. Vassallia,*, A. Gallinob, M. Weisc, W. von Scheidtc, L. Kappenbergera, L.K. von Segessera and J.-J. Goya on behalf of the Working Group Microcirculation of the European Society of Cardiology

a Divisions of Cardiology, Experimental Surgery, and Cardiovascular Surgery, University Hospital, Lausanne, Switzerland
b Ospedale San Giovanni, Bellinzona, Switzerland
c Medizinische Klinik und Poliklinik I, University Hospital Grosshadern, Munich, Germany

* Correspondence to: Dr Giuseppe Vassalli, Cardiologie BH-10, CHUV, 1011 Lausanne, Switzerland. Tel: +41-21-3140076; fax: +41-21-3140076
E-mail address: gvassall{at}hospvd.ch

Received 6 December 2002; revised 7 February 2003; accepted 6 March 2003

Abstract

Graft vasculopathy is an accelerated form of coronary artery disease that occurs in transplanted hearts. Despite major advances in immunosuppression, the prevalence of the disease has remained substantially unchanged during the last two decades. According to the ‘response to injury’ paradigm, graft vasculopathy is the result of a continuous inflammatory response to tissue injury initiated by both alloantigen-dependent and independent stress responses. Experimental evidence suggests that these responses may become self-sustaining, as allograft re-transplantation into the donor strain at a later stage fails to prevent disease progression. Histological evidence of endothelitis and arteritis, in association with intima fibrosis and atherosclerosis, reflects the central role of alloimmunity and inflammation in the development of arterial lesions. Experimental results in gene-targeted mouse models indicate that cellular and humoral immune responses are both involved in the pathogenesis of graft vasculopathy. Circulating antibodies against donor endothelium are found in a significant number of patients, but their pathogenic role is still controversial. Alloantigen-independent factors include donor-transmitted coronary artery disease, surgical trauma, ischaemia-reperfusion injury, viral infections, hyperlipidaemia, hypertension, and glucose intolerance. Recent therapeutic advances include the use of novel immunosuppressive agents such as sirolimus (rapamycin), HMG-CoA reductase inhibitors, calcium channel blockers, and angiotensin converting enzyme inhibitors. Optimal treatment of cardiovascular risk factors remains of paramount importance.

1. Introduction

Accelerated vascular disease is a characteristic feature of chronic graft dysfunction in organ transplantation. As such, accelerated coronary artery disease is one of the most discouraging aspects in heart transplantation.1,2The disease is the third leading cause of death, after infection and rejection, in the first year after heart transplantation, and the first leading cause of death in subsequent years. In a multi-institutional study, 42% of heart transplanted patients had abnormal coronary angiograms, and 7% of patients had severe coronaryartery disease by 5 years post-transplant.3Disease-related events including death and re-transplantation had an actuarial incidence of 7% at 5 years, and occurred in two of three patients with angiographically severe coronary artery disease. It should be noted that coronary angiography, which has been the main modality of invasive assessment of graft vasculopathy, is insensitive. Intravascular ultrasound (IVUS), which can detect early intimal thickening, has revealed a much higher incidence of the disease (up to 75% at 1 year after transplantation).4,5Virtually all 5-year survivors have histological evidence of graft vasculopathy.6

The first section of the present review briefly discusses the clinical aspects of cardiac allograft vasculopathy, with particular emphasis on endothelial dysfunction as an early manifestation of the disease. The main focus of the review is the pathogenesis of graft coronary vasculopathy, which involves both immunologic and nonimmunologic risk factors. Therapeutic approaches are briefly discussed in the final section.

2. Clinical aspects of graft vasculopathy

Classic angina as a symptom of graft coronary vasculopathy is rarely perceived because the transplanted heart is denervated. Consequently, the disease may be manifested by shortness of breath, decreased exercise capacity, syncope, arrhythmias, or heart failure. Unfortunately, the first manifestation may be acute myocardial infarction or sudden death. Therefore, patients should be evaluated on an annual basis for the presence of coronary artery disease. IVUS is more sensitive than coronary angiography with respect to early arterial lesions. Serial echocardiography is useful to detect progressive deterioration of left ventricular function as a result of myocardial ischaemia. Dobutamine stress echocardiography early after transplantation has been shown to predict development of graft vasculopathy and clinical events.7

2.1. Angiographic and histological findings
Angiographic features in patients with graft coronary vasculopathy are variable. Arterial lesions are typically concentric and involve the entire coronary tree, including the small intramyocardial branches. However, isolated lesions closely resembling atherosclerotic lesions in native vessels also occur. A classification system for luminal narrowing based on angiography was proposed by Gao and coworkers.8Category A referred to discrete, tubular lesions. Histological analysis showed that nearly half of type A lesions consisted of atheroma.9Category B denoted distal lesions that are usually characterized by fibrous intimal thickening, while category C referred to diffusely irregular patterns of narrowing. Fibrous intimal hyperplasia can be associated with arteritis with mononuclear cell infiltrates and obliterating endothelitis, eventually leading to destruction of elastic fibres and thinning of the muscular media.

The basic determinants of coronary narrowing are intimal thickening and vascular remodelling. Serial IVUS has shown that remodelling of the arterial wall can compensate for moderate intimal thickening.10,11Compensatory remodelling is greater in excentric than concentric lesions, possibly due to greater compliance of the normal portion of the vessel wall.11Besides compensatory enlargement, constrictive changes (negative remodelling) has also been identified and shown to be the most important predictor of the severity of focal stenoses.10Constrictive remodelling with a decrease in total vessel volume predominates in the first year after transplantation, whereas a slight compensatory enlargement can be observed at later time points. Recent data in a mouse model show that matrix metalloproteinases (MMPs) involved in the degradation and remodelling of extracellular matrix play an important role in constrictive vascular remodelling.12

2.2. Endothelial dysfunction as an early stage of graft vasculopathy
Endothelial dysfunction can be clinically detected as abnormal vasomotion in response to endothelium-dependent stimuli such as acetylcholine, substance P, the cold-pressure test, and dynamic exercise.13–15Reduced vasodilation, or paradoxical vasoconstriction, in response to acetylcholine occurs even in the absence of angiographic abnormalities.16Its predictive value is controversial. One study showed that acetylcholine-induced vasoconstriction early after transplantation may resolve over the following months, suggesting that it reflects a reversible insult to the endothelium around the time of transplantation.17This early insult involves ischaemia-induced release of cytokines such as interleukin (IL)-2 and IL-6, and the potent vasoconstrictor endothelin-1.18–20In another study, however, early vasomotor abnormalities predicted the development of graft vasculopathy at 1 year post-transplant.21Moreover, in a recent study using serial IVUS and Doppler flow-wire measurements, annual decrements in coronary endothelial function were associated with progressive intimal thickening, while abnormal vasomotor response to acetylcholine preceded the development of clinical endpoints.22Together, these observations suggest that endothelial dysfunction may represent an early and potentially reversible stage of graftvasculopathy. However, sustained endothelial dysfunction may reflect permanent vascular injury, with or without structural abnormalities.

Vasodilation during dynamic exercise depends on endothelial NO release. Both epicardial coronary vasodilation and coronary flow reserve during exercise were progressively impaired in cardiac transplant recipients 2–3 years post-transplant.23In contrast, pharmacological flow reserve was maintained. These results suggested progressive graft microvascular endothelial dysfunction in heart transplanted patients. However, coronary blood flow measurements by positron-emission tomography showed that coronary blood flow at rest is increased in transplanted patients and is responsible, at least in part, for decreased coronary flow reserve during exercise.24

3. Role of alloimmunity in the pathogenesis of graft vasculopathy

The simple observation that while graft coronary arteries develop vascular lesions, the host's native arteries are spared suggests a crucial role for alloimmunity in graft vasculopathy. This is consistent with experimental evidence that hearts transplanted into a genetically different recipient are affected, whereas those transplanted into a genetically identical recipient are spared. Furthermore, protocols that induce donor-specific immune tolerance prevent graft vasculopathy in experimental models.25

The number of HLA mismatches, as well as the number of rejection episodes and their duration have been identified as alloantigen-dependent risk factors.26,27However, differences in the long-term outcome between patients who experienced an acute rejection in the first year after heart transplantation and those who did not are small.28Thus, the relationship between acute cellular rejection and cardiac allograft vasculopathy remains controversial.29–31

3.1. Role of the endothelium in alloimmunity
Endothelial cells of coronary arteries are the first biological interface between the transplanted donor heart and circulating immunocompetent cells of the recipient. A variety of insults including brain death,32organ preservation and surgical trauma,33ischemia-reperfusion,34,35alloimmune responses to donor antigens,36cytomegalovirusinfection,37cyclosporine toxicity,38,39hyperlipidaemia and glucose intolerance40can ‘activate’ endothelial cells. The concept of ‘activated’ endothelium is not precisely defined, but it includes expression of major histocompatibility complex (MHC) molecules and adhesion molecules (e.g., E-selectin), secretion of cytokines and chemokines, and expression of molecules that provide costimulatory signals for T and B cell activation. In turn, activated CD4+T cells stimulate the expression of human leukocyte antigens (HLA) class-II molecules on endothelial cells, subsequent to HLA class-I detection by CD8+T cells. HLA and other donor antigens expressed on graft endothelial cells can elicit a sustained alloimmune reaction.41Clinical evidence suggests that HLA donor-recipient matching is an independent predictor of survival in heart transplantation.26In the Collaborative Transplant Study, cardiac transplant recipients receiving a graft with no or only one HLA-A, B, or DR mismatch (n=128 out of 8331; 1.5%) had a 83±4% 3-year graft survival rate as compared to 76±2% for those with two mismatches (n=439) and 71±1% for those with three to six mismatches (n=7764).42Although this association was highly significant (P<0.001), the impact on the clinical outcome was limited (6.6% difference in 3-year graft survival rates between two and three or more mismatches). In the clinical setting, donor organ shortage and the need for rapid transplantation in many patients with terminal heart failure do not allow for allocation of donor organs based on HLA matching. Nevertheless, information about HLA matching may be of some usefulness to guide early immunosuppression. Prospective HLA matching should be considered for retransplantation or in presensitized recipients.

Besides the well-established activation of the direct pathway of allorecognition,43endothelial cells can activate T cells via the indirect pathway, which involves processing and presentation of peptides derived from allogeneic HLA molecules by recipient antigen presenting cells (APCs) such as dendritic cells.41Importantly, dendritic cell invasion has been shown to be increased on activated endothelial cells and after blocking of the endothelial nitric oxide synthase.44Recently, it has been shown that direct CD8+T cell activation by endothelial cells can trigger acute cardiac allograftrejection.45

3.2. Cellular alloimmune responses
Experiments in rodent models of allograft vasculopathy have shown that arterial lesions first develop as endothelitis and subsequently progress to smooth muscle cell-rich fibrosis.46T cells (CD4+, CD8+, NK cells), macrophages, and dendritic cells have been evidenced in arterial lesions. These cells secrete a myriad inflammatory mediators including cell adhesion molecules, cytokines, chemokines, growth factors and macrophage activators, as well as proteases that degrade extracellular matrix proteins.

Depletion of CD4+, but not CD8+, T cells prevented arterial lesion formation in an experimental model.47Functional CD4+T cell responses have been subdivided in Th1- and Th2-type responses. Their respective roles were studied using mice deficient in interferon-{gamma} (IFN-{gamma}) or Stat4 (which regulate Th1-type responses) or in IL-10 (which mediates Th2-type responses) as graft recipients. Cardiac allografts placed in IFN-{gamma} or Stat4-deficient recipients had decreased graft vasculopathy, whereas those placed in IL-10-deficient recipients had increased vascular occlusion.48–50Increased vascular lesions were observed in recipient mice deficient in inducible nitric oxide synthase (iNOS) or transforming growth factor-ß (TGF-ß), suggesting an immunomodulatory role for these molecules.51,52

3.3. Humoral alloimmune responses
Both experimental and clinical studies have reported an association between antibody production after heart transplantation and graft vasculopathy. Heterotopic heart transplantation between mice bearing MHC class-I alone, class-II alone or minor mismatches, in combination with short immunosuppression, resulted in vascular lesions within 4–8 weeks.53Transplantation of B10.A mouse hearts into B10.BR recipients (MHC class-I mismatch only) resulted in high-titer anti-donor antibody production and severe graft vasculopathy.54Conversely, low-titer anti-donor antibodies and mild arterial disease were observed in the reciprocal donor-recipient strain combination. However, graft vasculopathy in this combination was induced by treating recipients with an anti-donor antiserum made in a separate strain. Furthermore, hearts transplanted into B cell-deficient mice that are incapable of producing immunoglobulins developed only minor disease.55Hearts transplanted into immunodeficient SCID mice survived indefinitely with no significant vasculopathy. However, vascular lesions rich in macrophages and NK cells developed in SCID mice upon treatment with an antiserum reactive with donor antigens. Together, these findings demonstrate that humoral responses play a key role in the pathogenesis of graft vasculopathy, but cellular responses are also involved.

In clinical heart transplantation, circulating anti-HLA antibodies have been associated with poor survival.56,57Anti-endothelial antibodies detected at 1 and 2 years post-transplant were found in patients who had developed graft vasculopathy at this time.58These antibodies were reactive with as many as 40 peptides from endothelial cells.59The most abundant of these antibodies were reactive with the intermediate filament vimentin and were associated with graft vasculopathy. Antibodies against endothelial cell surface molecules such as MHC class-I and intercellular adhesion molecule (ICAM)-1 were associated with endothelial activation and release of growth factors.60,61Increasing evidence indicates that a large number of potential antigens are released from the allograft to be processed and presented via the indirect pathway by recipient APCs.62Antibody responses against non-HLA and minor antigens have been reported.58,59,63

4. Role of alloantigen-independent factors in the pathogenesis of graft vasculopathy

According to the ‘immunologic view’, centred on the overwhelming importance of alloimmunity, graft vasculopathy has long been referred to as chronic rejection. However, this term is misleading because it does not adequately take alloantigen-independent factors into account. Alternatively, the ‘response to injury’ concept, first formulated as an explanation for naturally occurring atherosclerosis,64may provide a theoretical framework for understanding graft vasculopathy as well. This concept dictates that vascular lesions are the result of cumulative vessel injury induced both by alloimmune responses and by nonspecific insults. Endothelial injury triggers a cascade of ‘tissue repair’ mechanisms that involve vascular cell proliferation, fibrosis, and vascular remodelling. However, exuberant ‘tissue repair’ leads to intimal thickening and luminal narrowing. At a later stage, nonspecific mechanisms may become self-sustaining and promote arterial lesion progression even in an immunologically friendly environment, as experimental late allograft re-transplantation back into the donor strain does not prevent progression of the disease.65,66

4.1. Nonimmunologic risk factors
Studies evaluating the contribution of nonimmunologic risk factors to graft vasculopathy have reported variable results. A multi-institutional coronary angiography study identified donor characteristics such as older age, male gender and hypertension, as well as recipient characteristics such as older age and male gender as risk factors.3Moreover, multicentre IVUS study identified older donor age and recipient body mass index as risk factors for coronary intimal thickening.67

4.2. Input injury
‘Input injury’ designates the burden in the organ at the time of transplantation. It includes both donor-transmitted disease and graft injury as a result of brain death, donor maintenance, organ removal and preservation, and surgical trauma.33Studies on kidney transplantation have shown that organs from live donors, even in an immunologic mismatch setting, have a significant advantage over cadaveric donors.32Pre-existing coronary artery lesions are not infrequent, even in young donors (56% of donors aged 32±12 years, as assessed by IVUS). However, donor-transmitted lesions do not seem to enhance accelerated graft vasculopathy after heart transplantation.68

4.3. Ischaemia-reperfusion injury
Interruption of blood supply during ischaemia leads to anaerobic metabolism, depletion of adenosine-triphosphate (ATP), dysfunction of membrane ionic ATP-dependent pumps, entry of calcium and sodium into the cell. Upon reperfusion, highly reactive hydroxil radicals are generated, which stimulate P-selectin expression on endothelial cells. Activated endothelial cells also produce platelet activating factor (PAF) that interacts with the PAF receptor on neutrophils.34Acting in concert, PAF and P-selectin promote neutrophil activation and induce ß2-integrin expression, resulting in ß2-integrin binding to ICAM, which mediates firm attachment of neutrophils to endothelial cells. Together, these observations suggest that ischaemia/reperfusion injury plays a major role in graft vasculopathy.

4.4. Cytokines and chemokines
Cytokines are secreted pro-inflammatory molecules that regulate leukocyte activation. The Th1 subset of CD4+cells produces IFN-{gamma}, IL-2, and TGF-ß1, whereas the Th2 subset produces IL-4, IL-5, IL-6, IL-9, IL-10, and IL-13. As mentioned, IFN-{gamma} seems to promote, whereas IL-10 protects against graft vasculopathy.48,50Chemokines (chemoattractant cytokines) regulate the recruitment of leukocytes to the allograft.69Expression of several chemokines including monocyte chemoattractant protein (MCP)-1, MCP-3, IL-8 and RANTES was demonstrated in transplanted human hearts. RANTES production promoted monocyte adhesion to activated endothelium and arterial lesion formation in a graft vasculopathy model.70Mice deficient in the CC chemokine receptors (CCRs)-1 and 5 had markedly attenuated cardiac allograft rejection in the absence of immunosuppression.71Short-term treatment with low-dose cyclosporine, which failed to prevent rejection in wildtype mice, induced indefinite allograft acceptance with no significant vasculopathy in CCR-1-deficient mice. Consistently, administration of a CCR-1 antagonist delayed heart transplant rejection in an experimental model.72These results suggest an important role for chemokines in allograft rejection andvasculopathy.

4.5. Cytomegalovirus (CMV) infection
CMV infection, the most frequent infectious complication in transplanted patients, can cause vascular inflammation (endothelitis and arteritis). Both clinical and experimental evidence points toward a role for CMV in the pathogenesis of graft atherosclerosis.73–76Prophylactic therapy with ganciclovir has reduced the incidence of CMV disease, but not in the group at highest risk (i.e., seronegative recipients of grafts from seropositive donors). In a post-hoc analysis, ganciclovir prophylaxis was associated with decreased intimal thickening, reduced coronary artery disease and improved survival.77Moreover, CMV hyperimmune globulin in combination with ganciclovir may be more protective than ganciclovir alone.78These issues need to be further addressed in prospective, randomized trials.

4.6. Metabolic factors
Last but not least, conventional vascular risk factors such as hyperlipidaemia, glucose intolerance and hypertension, which are highly prevalent in transplanted patients on current immunosuppressive regimens, play contributory roles in graft endothelial dysfunction and transplant vasculopathy.79Presence of multiple vascular risk factors was associated with severe impairment of coronary vasodilation during exercise in cardiac transplant recipients.80At necropsy, histological analysis of transplanted hearts showed frequent atheromata with diffuse intra- and extra-cellular lipid accumulation in both intimal and medial walls.81Mean total cholesterol content in coronary arteries was more than 10-fold higher than in comparable donor age-matched native vessels. Extent of lipids in the arterial walls was highly correlated with meancumulative cyclosporine and prednisone doses.81Thus, the importance of metabolic factors in the development of graft vasculopathy should be emphasized, particularly because effective treatments for these risk factors are available.

5. Therapeutic approaches to graft vasculopathy

The optimal treatment prophylaxis for graft vasculopathy has not been established. Current treatments are moderately effective in delaying the development of arterial lesions, but they do not completely prevent it. Experimental evidence that improved immunosuppression can prevent graft vasculopathy suggests that optimized immunosuppression is a primary goal in treatment prophylaxis of the disease.25

Most current protocols are based on cyclosporine-A or tacrolimus (FK506), calcineurin inhibitors that block early T-cell activation, and on the purine synthesis inhibitors azathioprine and mycophenolate mofetil. In most centres, steroids are weaned when endomyocardial biopsies show low or negative rejection scores. Most cardiac transplant recipients can be maintained on steroid-free regimens, thus avoiding the detrimental metabolic effects of these drugs.82Low-dose cyclosporine protocols have been evaluated inan attempt to reduce endothelial toxicity; however cyclosporine dose reduction at 1 year post-transplant was not associated with improved coronary artery diameter at 2 and 3 year follow- up.83These negative results may be due to the late onset of low-dose cyclosporine, as initial lesions develop during the first year post-transplant. This is consistent with another report showing that augmented immunosuppression started in the first year post-transplant is associated with arterial lesion regression in 92% of patients, as compared to 40% when started in the second year post-transplant.84Daclizumab, a hybrid humanized interleukin-2 receptor antibody, has been effective in preventing allograft rejection in clinical hearttransplantation.85The immunosuppressive and anti-proliferative drug sirolimus (rapamycin), an inhibitor of interleukin-2-mediated signal transduction pathways, can be used as a rescue drug when cyclosporine is contraindicated or ineffective.86Sirolimus has been shown to reverse graft vasculopathy in experimental studies and initial clinical trials.87–89Preliminary results of an ongoing multicentre trial suggest that sirolimus treatment is associated with reduced coronary artery disease in cardiac transplant recipients.89If the beneficial effects of sirolimus are confirmed by definitive results, this drug may represent a major advance in the prevention of graft vasculopathy.

Only a few small trials have compared different immunosuppressive regimens for prevention of graft vasculopathy. The combination of tacrolimus and mycophenolate mofetil was superior to tacrolimus and azathioprine, and comparable to cyclosporine and azathioprine, with respect to coronary vasomotor function early after transplantation; however, this combination failed to reduce coronary intimal thickening.90Another study showed no significant differences in vascularocclusion between mycophenolate mofetil and azathioprine immunosuppression.91In a prospective IVUS trial, cyclosporine was slightly, although not significantly, more effective than tacrolimus in preventing graft vasculopathy in the first year post-transplant.92

The calcium channel blocker diltiazem started early after transplantation was associated with reduced coronary artery narrowing, reduced mortality from graft arteriosclerosis, and reduced overall mortality at 1 year post-transplant.93Angiotensin-converting enzyme (ACE) inhibitors may also be effective in delaying development of graft vasculopathy.94

The only established clinical treatment is routine therapy with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) inhibitors (statins). Pravastatin improved 1-year survival in a prospective study.95Notably, protection was independent of changes in lipid levels, probably reflecting immunomodulation such as reduced natural killer cell cytotoxicity,95decreased cytokine activity and/or improved coronary endothelial function.96Simvastatin reduced graft coronary artery disease and overall mortality after heart transplantation in a 4-year follow-up trial.97

Once transplant vasculopathy is manifest, percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass grafting (CABG) offer palliative options in cases characterized by a single or a few focal lesions, as opposed to diffuse luminal narrowing.98,99Although restenosis was typically more frequent in dilated graft versus native coronary lesions, IVUS studies have identified extensive early recoil as a major cause for restenosis in cardiac transplant recipients.99Consequently, intravascular stent implantation recently resulted in improved outcome in patients with focal coronary obstruction. In a single centre experience, treatment of 41 patients (75 lesions, 85 stents) resulted in a success rate of 98% with a 6-month restenosis rate of 14%.99A similar restenosis rate (18%) after stent implantation was reported by another one-centre study, which favourably compared to a 60% restenosis rate with PTCA in the absence of stenting.100Although only limited experience is available regarding the surgicalapproach with CABG, this should be considered in selected patients with focal coronary lesions not suitable for PTCA.

In summary, both alloantigen-dependent and independent factors are involved in the development of cardiac allograft arteriopathy. Treatment prophylaxis with HMG-CoA reductase inhibitors and, possibly, calcium channel blockers and ACE inhibitors may delay arterial occlusion. Preliminary clinical results using sirolimus are very encouraging,89and long-term results of an ongoing multicentre trial with this drug are eagerly awaited. Novel immunomodulating approaches (e.g., T-cell costimulatory blockade with CTLA4-Ig or CD40-Ig) have shown promising effects in experimental models. Optimized treatment of non-immunologic cardiovascular risk factors remains of paramount importance.

Acknowledgments

Support by the Lausanne Heart Transplant Foundation, the Swiss National Science Foundation, the Swiss Cardiology Foundation, and the Teo Rossi di Montelera Foundation (Lausanne) is acknowledged.

References

  1. Valantine HA, Schroeder JS. Recent advances in cardiac transplantation. N Engl J Med. 1995;333:660–661.[Free Full Text]
  2. Weis M, von Scheidt W. Cardiac allograft vasculopathy: a review. Circulation. 1997;96:2069–2077.[Abstract/Free Full Text]
  3. Costanzo MR, Naftel DC, Pritzker MR et al. Heart transplant coronary artery disease detected by coronary angiography: a multiinstitutional study of preoperative donor and recipient risk factors. Cardiac transplant research database. J Heart Lung Transplant. 1998;17:744–753.[ISI][Medline]
  4. Anderson TJ, Meredith IT, Uehata A et al. Functional significance of intimal thickening as detected by intravascular ultrasound early and late after cardiac transplantation. Circulation. 1993;88:1093–1100.[Abstract]
  5. Yeung AC, Davis SF, Hauptman PJ et al. Incidence and progression of transplant coronary artery disease over 1 year: results of a multicenter trial with use of intravascular ultrasound. J Heart Lung Transplant. 1995;14:S215–S220.[ISI][Medline]
  6. Johnson DE, Gao SZ, Schroeder JS et al. The spectrum of coronary artery pathologic findings in human cardiac allografts. J Heart Transplant. 1989;8:349–359.[ISI][Medline]
  7. Akosah KO, McDaniel S, Hanrahan JS et al. Dobutamine stress echocardiography early after heart transplantation predicts development of allograft coronary artery disease and outcome. J Am Coll Cardiol. 1998;31:1607–1614.[CrossRef][ISI][Medline]
  8. Gao SZ, Alderman EL, Schroeder JS et al. Accelerated coronary vascular disease in the heart transplant patient: coronary arteriographic findings. J Am Coll Cardiol. 1988;12:334–340.[ISI][Medline]
  9. Johnson DE, Alderman EL, Redwood DR et al. Transplant coronary disease: Histopathologic correlations with angiographic morphology. J Am Coll Cardiol. 1991;17:449–457.[ISI][Medline]
  10. Pethig K, Heublein B, Meliss RR et al. Volumetric remodeling of the proximal left coronary artery: early versus late after heart transplantation. J Am Coll Cardiol. 1999;34:197–203.[CrossRef][Medline]
  11. Schwarzacher SP, Uren NG, Ward MR et al. Determinants of coronary remodeling in transplant coronary disease: asimultaneous intravascular ultrasound and Doppler flow study. Circulation. 2000;101:1384–1389.[Abstract/Free Full Text]
  12. Tsukioka K, Suzuki J, Fujimori M et al. Expression of matrix metalloproteinases in cardiac allograft vasculopathy and its attenuation by anti MMP-2 ribozyme gene transfection. Cardiovasc Res. 2002;56:472–478.[CrossRef][ISI][Medline]
  13. Fish RD, Nabel EG, Selwyn AP et al. Responses of coronary arteries of cardiac transplant patients to acetylcholine. J Clin Invest. 1988;81:21–31.[ISI][Medline]
  14. Mugge A, Heublein B, Kuhn M et al. Impaired coronary dilator responses to substance P and impaired flow-dependent dilator responses in heart transplant patients with graft vasculopathy. J Am Coll Cardiol. 1993;21:163–170.[ISI][Medline]
  15. Benvenuti C, Aptecar E, Mazzucotelli JP et al. Coronary artery response to cold-pressure test is impaired early after operation in heart transplant recipients. J Am Coll Cardiol. 1995;26:446–451.[CrossRef][ISI][Medline]
  16. Nitenberg A, Benvenuti C, Aptecar E et al. Acetylcholine-induced constriction of angiographically normal coronary arteries is not time dependent in transplant recipients. J Am Coll Cardiol. 1993;22:151–158.[Medline]
  17. Aptecar E, Benvenuti C, Loisance D et al. Early impairment of acetylcholine-induced endothelium-dependent coronary vasodilation is not predictive of secondary graft atherosclerosis. Chest. 1995;107:1266–1274.[Abstract/Free Full Text]
  18. Weis M, Wildhirt SM, Schulze C et al. Modulation of coronary vasomotor tone by cytokines in cardiac transplant recipients. Transplantation. 1999;68:1263–1267.[CrossRef][Medline]
  19. Weis M, Wildhirt SM, Schulze C et al. Endothelin in coronary endothelial dysfunction early after human heart transplantation. J Heart Lung Transplant. 1999;18:1071–1079.[CrossRef][Medline]
  20. Ravalli S, Szabolcs M, Albala A et al. Increased immunoreactive endothelin-1 in human transplant coronary artery disease. Circulation. 1996;94:2096–2102.[Abstract/Free Full Text]
  21. Davis SF, Yeung AC, Meredith IT et al. Early endothelial dysfunction predicts the development of transplant coronary artery disease at 1 year posttransplant. Circulation. 1996;93:457–462.[Abstract/Free Full Text]
  22. Hollenberg SM, Klein LW, Parrillo JE et al. Coronary endothelial dysfunction after heart transplantation predicts allograft vasculopathy and cardiac death. Circulation. 2001;104:3091–3096.[Abstract/Free Full Text]
  23. Vassalli G, Gallino A, Kiowski W et al. Reduced coronary flow reserve during exercise in heart transplant recipients. Circulation. 1997;95:607–613.[Abstract/Free Full Text]
  24. Krivokapich J, Stevenson L, Kobashigawa J et al. Quantification of absolute myocardial perfusion at rest and during exercise with positron emission tomography after human cardiac transplantation. J Am Coll Cardiol. 1991;18:512–517.[Medline]
  25. Orloff MS, DeMara EM, Coppage ML et al. Prevention of chronic rejection and graft arteriosclerosis by tolerance induction. Transplantation. 1995;59:282–288.[ISI][Medline]
  26. Hosenpud JD, Edwards EB, Lin H-M et al. Influence of HLA matching on thoracic transplant outcome. An analysis from UNOS/ISHLT thoracic registry. Circulation. 1996;94:170–174.[Abstract/Free Full Text]
  27. Costanzo-Nordin MR. Cardiac allograft vasculopathy: relationship with acute cellular rejection and histocompatibility. J Heart Lung Transplant. 1992;11:S90–S103.[ISI][Medline]
  28. Opelz G. Critical evaluation of the association of acute with chronic graft rejection in kidney and heart transplant recipients. The Collaborative Transplant Study. Transplant Proc. 1997;29:73–76.[CrossRef][ISI][Medline]
  29. Salomon RN, Hughes CC, Schoen FJ et al. Human coronary transplantation-associated arteriosclerosis. Evidence for a chronic immune reaction to activated graft endothelial cells. Am J Pathol. 1991;138:791–798.[Abstract]
  30. Libby P, Tanaka H. The pathogenesis of coronary arteriosclerosis (‘chronic rejection’) in transplanted hearts. Clin Transplant. 1994;8:313–318.[Medline]
  31. Hauptmann PJ, Nakagawa T, Tanaka H et al. Acute rejection: culprit or coincidence in the pathogenesis of cardiac graft vascular disease? J Heart Lung Transplant. 1995;14:S173–S180.[Medline]
  32. Terasaki PI, Cecka JM, Gjertson DW et al. High survival rates of kidney transplants from spousal and living unrelated donors. N Engl J Med. 1995;333:333–336.[Abstract/Free Full Text]
  33. Halloran PF. Non-immunologic tissue injury and stress in chronic allograft dysfunction. Graft. 1998;1:25–29.
  34. Grinyò JM. Reperfusion injury. Transplant Proc. 1977;29:59–62.[CrossRef]
  35. Fellström B, Akyürek ML, Larsson F et al. Ischemia induced upregulation of growth factor expression in experimental transplant arteriosclerosis. Transplant Proc. 1977;29:2558.[CrossRef]
  36. Hutchison IV. Cardiac allograft vasculopathy–the cellular attack. Z Kardiol. 2000;89(Suppl 9):IX/16–IX.[CrossRef]
  37. Grattan MT, Moreno-Cabral CE, Starnes VA et al. Cytomegalovirus infection is associated with cardiac allograft rejection and atherosclerosis. JAMA. 1989;261:3561–3566.[Abstract]
  38. Sudhir K, MacGregor JS, DeMarco T et al. Cyclosporinimpairs release of endothelium-derived relaxing factors in epicardial and resistance coronary arteries. Circulation. 1994;90:3018–3023.[Abstract]
  39. Sata M, Walsh K. Cyclosporine downregulates Fas ligand expression on vascular endothelial cells: Implication for accelerated vasculopathy by immunosuppressive therapy. Biochem Biophys Res Comm. 1999;263:430–432.[CrossRef][Medline]
  40. Hoang K, Chen YD, Reaven G et al. Diabetes and dyslipidemia. A new model for transplant coronary artery disease. Circulation. 1998;97:2160–2168.[Abstract/Free Full Text]
  41. Briscoe DM, Alexander SI, Lichtman AH. Interactions between T lymphocytes and endothelial cells in allograft rejection. Curr Opin Immunol. 1998;10:525–531.[CrossRef][Medline]
  42. Opelz G, Wujciak T. The influence of HLA compatibility on graft survival. Collaborative Transplant Study. N Engl J Med. 1994;330:816–819.[Abstract/Free Full Text]
  43. Auchincloss H Jr, Sultan H. Antigen processing and presentation in transplantation. Curr Opin Immunol. 1996;8:681–687.[CrossRef][ISI][Medline]
  44. Weis M, Schlichting CL, Engleman EG et al. Endothelial determinants of dendritic cell adhesion and migration: new implications for vascular diseases. Arterioscler Thromb Vasc Biol. 2002;22:1817–1823.[Abstract/Free Full Text]
  45. Kreisel D, Krupnick AS, Gelman AE et al. Non-hematopietic allograft cells directly activate CD8+ T cells and trigger acute rejection: An alternative mechanism of allorecognition. Nat Med. 2002;8:233–239.[CrossRef][ISI][Medline]
  46. Adams DH, Wyner LR, Karnovsky MJ. Experimental graft arteriosclerosis: Immunocytochemical analysis of lesion development. Transplantation. 1993;56:794–799.[Medline]
  47. Szeto WY, Krasinskas AM, Kreisel D et al. Depletion of recipient CD4+ but not CD8+ T lymphocytes prevents the development of cardiac allograft vasculopathy. Transplantation. 2002;73:1116–1122.[CrossRef][Medline]
  48. Raisanen-Sokolowski A, Glysing-Jensen T, Koglin J et al. Reduced transplant arteriosclerosis in murine cardiac allografts placed in interferon-gamma knockout recipients. Am J Pathol. 1998;152:359–365.[Abstract]
  49. Koglin J, Glysing-Jensen T, Gadiraju S et al. Attenuated cardiac allograft vasculopathy in mice with targeted deletion of the transcription factor stat 4. Circulation. 2000;101:1034–1039.[Abstract/Free Full Text]
  50. Raisanen-Sokolowski A, Glysing-Jensen T, Russell ME. Leukocyte-suppressing influences of interleukin (IL)-10 in cardiac allografts: insights from IL-10 knockout mice. Am J Pathol. 1998;153:1491–1500.[Abstract/Free Full Text]
  51. Koglin J, Glysing-Jensen T, Mudgett JS et al. Exacerbated transplant arteriosclerosis in inducible nitric oxide-deficient mice. Circulation. 1998;97:2059–2065.[Abstract/Free Full Text]
  52. Koglin J, Glysing-Jensen T, Raisanen-Sokolowski A et al. Immune sources of transforming growth factor-beta 1 reduce transplant arteriosclerosis: insights from a knockout mouse model. Circ Res. 1998;83:652–660.[Abstract/Free Full Text]
  53. Russell PS, Chase CM, Winn HJ et al. Coronary atherosclerosis in transplanted rat hearts. I. Time course and immunogenetic and immunopathological considerations. Am J Pathol. 1994;144:260–274.[Abstract]
  54. Russell PS, Chase CM, Winn HJ et al. Coronary atherosclerosis in transplanted rat hearts. II. Time course and immunogenetic and immunopathological considerations. J Immunol. 1994;152:5135–5141.[Abstract/Free Full Text]
  55. Russell PS, Chase CM, Colvin RB. Alloantibody and T cell mediated immunity in the pathogenesis of transplantarteriosclerosis. Lack of progression to sclerotic lesions in B cell deficient mice. Transplantation. 1997;64:1531–1536.[Medline]
  56. Suciu-Foca N, Reed E, Marboe C et al. The role of anti-HLA antibodies in heart transplantation. Transplantation. 1991;51:716–724.[ISI][Medline]
  57. Reed EF, Hong B, Ho E, Harris PE et al. Monitoring of soluble HLA alloantigens and anti-HLA antibodies identifies heart allograft recipients at risk of transplant-associated coronary artery disease. Transplantation. 1996;61:566–572.[ISI][Medline]
  58. Dunn MJ, Crisp S, Rose ML et al. Antiendothelial antibodies and coronary artery disease after cardiac transplantation. Lancet. 1992;339:1566–1570.[ISI][Medline]
  59. Wheeler C, Collins A, Dunn MJ et al. Identification of antiendothelial antibodies associated with accelerated coronary artery disease after cardiac transplantation. J Heart Lung Transplant. 1995;14:188–197.
  60. Harris PE, Bian H, Reed EF. Induction of high affinity fibroblast growth factor receptor expression and proliferation in human endothelial cells by anti-HLA antibodies: a possible mechanism for transplant atherosclerosis. J Immunol. 1997;159:5697–5704.[Abstract]
  61. Lawson C, Ainsworth M, Yacoub MH et al. Ligation of ICAM-1 on endothelial cells leads to expression of VCAM-1 via a nuclear factor kappa B independent mechanism. J Immunol. 1999;162:2990–2996.[Abstract/Free Full Text]
  62. Rose ML. Role of antibodies in transplant-associated cardiac allograft vasculopathy. Z Kardiol. 2000;89(Suppl 9):IX/11–IX.[CrossRef]
  63. Ferry BL, Welsh KI, Dunn MJ et al. Anti-cell surface endothelial antibodies in sera from cardiac and kidney transplant recipients: association with chronic rejection. Transplant Immunol. 1997;5:17–24.[CrossRef][ISI][Medline]
  64. Ross R. The pathogenesis of atherosclerosis: an update. N Engl J Med. 1986;314:488–541.[ISI][Medline]
  65. Izutani H, Miyagawa S, Shirakura R et al. Evidence that graft coronary arteriosclerosis begins in the early phase after transplantation and progresses without chronic immunoreaction. Histopathological analysis using a retransplantation model. Transplantation. 1995;60:1073–1079.[ISI][Medline]
  66. Forbes RD, Zheng SX, Gomersall M et al. Irreversible chronic vascular rejection occurs only after development ofadvanced allograft vasculopathy: a comparative study of a rat cardiac allograft model using a retransplantation protocol. Transplantation. 1997;63:743–749.[CrossRef][Medline]
  67. Hauptman PJ, Davis SF, Miller Lxppstopnospacexpppx, On behalf of the multicenter intravascular ultrasound transplant study group et al. The role of nonimmune risk factors in the development and progression of graft arteriosclerosis: preliminary insights from a multicenter intravascular ultrasound study. J Heart Lung Transplant. 1995;14:S238–S242.[ISI][Medline]
  68. Kapadia SR, Nissen SE, Guetta V et al. Development of transplant vasculopathy and progression of donor-transmitted atherosclerosis: a comparison by serial intravascular ultrasound imaging. Circulation. 1998;98:2672–2678.[Abstract/Free Full Text]
  69. Hancock WW, Gao W, Faia KL et al. Chemokines and their receptors in allograft rejection. Curr Opin Immunol. 2000;12:511–516.[CrossRef][ISI][Medline]
  70. Yun JJ, Fischbein MP, Laks H et al. Rantes production during development of cardiac allograft vasculopathy. Transplantation. 2001;71:1649–1656.[Medline]
  71. Gao W, Topham PS, King JA et al. Targeting of the chemokine receptor CCR1 suppresses development of acute and chronic cardiac allograft rejection. J Clin Invest. 2000;105:35–44.[Abstract/Free Full Text]
  72. Horuk R, Clayberger C, Krensky AM et al. A non-peptide functional antagonist of the CCR1 chemokine receptor is effective in rat heart transplant rejection. J Biol Chem. 2001;276:4199–4204.[Abstract/Free Full Text]
  73. Grattan MT, Moreno-Cabral CE, Starnes VA et al. Cytomegalovirus infection is associated with cardiac allograft rejection and atherosclerosis. JAMA. 1989;261:3561–3566.[Abstract]
  74. Kendall TJ, Wilson JE, Radio SJ et al. Cytomegalovirus and other herpesviruses: do they have a role in the development of accelerated coronary arterial disease? J Heart Lung Transplant. 1992;11:S14–S20.[Medline]
  75. Koskinen P, Lemstrom K, Bruning H et al. Cytomegalovirus infection induces vascular wall inflammation and doubles arteriosclerotic changes in rat cardiac allografts. Transplant Proc. 1995;27:574–575.[Medline]
  76. Lemstroem KB, Bruning JH, Bruggeman CA et al. Cytomegalovirus infection-enhanced allograft arteriosclerosis is prevented by DHPG prophylaxis in the rat. Circulation. 1994;90:1969–1978.[Abstract]
  77. Valantine HA, Gao SZ, Menon SG et al. Impact of prophylactic immediate posttransplant ganciclovir on development of transplant atherosclerosis: a post hoc analysis of a randomized, placebo-controlled study. Circulation. 1999;100:61–66.[Abstract/Free Full Text]
  78. Valantine HA, Luikart H, Doyle RL et al. Impact of cytomegalovirus hyperimmune globulin on outcome after cardiothoracic transplantation: a comparative study of combined prophylaxis with CMV hyperimmune globulin plus ganciclovir versus ganciclovir alone. Transplantation. 2001;72:1647–1652.[CrossRef][Medline]
  79. Kemna MS, Valantine HA, Hunt SA et al. Metabolic risk factors for atherosclerosis in heart transplant recipients. Am Heart J. 1994;128:68–72.[CrossRef][ISI][Medline]
  80. Vassalli G, Bracht C, Gallino A et al. Coronary vasomotion and flow reserve after heart transplantation. Morton M. Annual Cardiac Surgery. 8th edn. London: Morton M, International Thomson Company; 1995. .
  81. McManus BM, Horley KJ, Wilson JE et al. Prominence of coronary arterial wall lipids in human heart allografts. Implications for pathogenesis of allograft arteriopathy. Am J Pathol. 1995;147:293–308.[Abstract]
  82. Seydoux C, Berguer DG, Stumpe F et al. Does early steroid withdrawal influence rejection and infection episodes during the first 2 years after heart transplantation? Transplant Proc. 1997;29:620–624.[CrossRef][Medline]
  83. Vassalli G, Kaski JC, Tousoulis D et al. Low-dose cyclosporine treatment fails to prevent coronary luminal narrowing after heart transplantation. J Heart Lung Transplant. 1996;15:612–619.[Medline]
  84. Lamich R, Ballester M, Martì V et al. Efficacy of augmented immunosuppressive therapy for early vasculopathy in heart transplantation. J Am Coll Cardiol. 1998;32:413–419.[CrossRef][Medline]
  85. Beniaminovitz A, Itescu S, Lietz K et al. Prevention of rejection in cardiac transplantation by blockade of the interleukin-2 receptor with a monoclonal antibody. N Engl J Med. 2000;342:613–619.[Abstract/Free Full Text]
  86. Snell GI, Levvey B, Chin W et al. Rescue therapy: a role for sirolimus in lung and heart transplant recipients. Transplant Proc. 2001;33:1084–1085.[CrossRef][ISI][Medline]
  87. Poston RS, Billingham M, Hoyt EG et al. Rapamycin reverses chronic graft vascular disease in a novel cardiac allograft model. Circulation. 1999;100:67–74.[Abstract/Free Full Text]
  88. Goggins WC, Fisher RA, Cohen DS et al. Effect of single-dose rapamycin-based immunosuppression on the development of cardiac allograft vasculopathy. J Heart Lung Transplant. 1996;15:790–795.[Medline]
  89. Mancini D, Pinney S, Burkoff D et al. Use of rapamycin slows progression of cardiac transplant vasculopathy. Circulation. 2001;0:3370 Suppl. Abstract..
  90. Weis M, Wildhirt SM, Schulze C et al. Coronary vasomotor dysfunction in the cardiac allograft. Impact of different immunosuppressive regimens. J Cardiovasc Pharmacol. 2000;36:776–784.[CrossRef][Medline]
  91. Kobashigawa J, Miller L, Renlund D et al. A randomized active-controlled trial of mycophenolate mofetil in heart transplant recipients. Transplantation. 1998;66:507–515.[ISI][Medline]
  92. Klauss V, König A, Spes C et al. Cyclosporine versus tacrolimus (FK506) for prevention of cardiac allograft vasculopathy. Am J Cardiol. 2000;85:266–269.[CrossRef][ISI][Medline]
  93. Schroeder JS, Gao S-Z, Alderman EL et al. A preliminary study of diltiazem in the prevention of coronary artery disease in heart-transplant recipients. N Engl J Med. 1993;328:164–170.[Abstract/Free Full Text]
  94. Mehra MR, Ventura HO, Chambers R et al. An intravascular ultrasound study of the influence of angiotensin-converting enzyme inhibitors and calcium entry blockers on the development of cardiac allograft vasculopathy. Am J Cardiol. 1995;72:853–854.[CrossRef]
  95. Kobashigawa JA, Katznelson S, Laks H et al. Effect of pravastatin on outcomes after cardiac transplantation. N Engl J Med. 1995;333:621–627.[Abstract/Free Full Text]
  96. Weis M, Pehlivanli S, Meiser BM et al. Simvastatin treatment is associated with improvement in coronary endothelial function and decreased cytokine activation in patients after heart transplantation. J Am Coll Cardiol. 2001;38:814–818.[CrossRef][Medline]
  97. Wenke K, Meiser B, Thiery J et al. Simvastatin reduces graft vessel disease and mortality after heart transplantation. Circulation. 1997;96:1398–1402.[Abstract/Free Full Text]
  98. Von Scheidt W, Uberfuhr P, Reichart B et al. The role of PTCA in the management of focal critical lesions in transplant coronary artery disease. Transplant Proc. 1995;3:1936–1938.
  99. Pethig K, Heublein B, Haverich A. Cardiac allograft vasculopathy-coronary interventions and surgical options. Z Kardiol. 2000;89(Suppl 9):IX/66–IX.[CrossRef]
  100. Aranda JM, Pauly DF, Kerensky RA et al. Percutaneous coronary intervention versus medical therapy for coronary allograft vasculopathy. One center's experience. J Heart Lung Transplant. 2002;21:860–866.[CrossRef][Medline]