Specificity of lymphocytotoxic antibodies formed after cardiac transplantation and correlation with rejection episodes

Extracorporeal photopheresis and its role in heart transplant rejection: prophylaxis and treatment

Heart transplantation is the gold standard therapeutic option for select patients with end-stage heart failure. Unfortunately, successful long-term outcomes of heart transplantation can be hindered by immune-mediated rejection of the cardiac allograft, specifically acute cellular rejection, antibody-mediated rejection, and cardiac allograft vasculopathy. Extracorporeal photopheresis is a cellular immunotherapy that involves the collection and treatment of white blood cells contained in the buffy coat with a photoactive psoralen compound, 8-methoxy psoralen, and subsequent irradiation with ultraviolet A light. This process is thought to cause DNA and RNA crosslinking, ultimately leading to cell destruction. The true mechanism of therapeutic action remains unknown. In the last three decades, extracorporeal photopheresis has shown promising results and is indicated for a variety of conditions. The American Society for Apheresis currently recommends the use of extracorporeal photopheresis for the treatment of cutaneous T-cell lymphoma, scleroderma, psoriasis, pemphigus vulgaris, atopic dermatitis, graft-versus-host disease, Crohn's disease, nephrogenic systemic fibrosis, and solid organ rejection in heart, lung, and liver transplantation. In this review, we aim to explore the proposed effects of extracorporeal photopheresis and to summarize published data on its use as a prophylactic and therapy in heart transplant rejection.

Plasma Exchange and Immunoadsorption of Patients with Thoracic Organ Transplantation

Primary organ failure after transplantation (TX) remains a serious complication and leads to a high percentage of lethality. It is known, however, that the speed of rejection and tissue destruction depends on 3 main factors: antibody titer, the ability of the tissue to repair itself, and immunosuppressive measures. Especially with evidence for antibodies against human leukocyte antigen (HLA-ab), the immunological risk of persistent and acute episodes of rejection increases. The role of non-HLA-ab in rejection episodes is often underestimated and should be studied further. Antibody-mediated rejection (AMR) is still an unsolved problem in thoracic organ TX. An essential pillar of antihumoral therapy are the extracorporeal procedures like plasmapheresis (PP), therapeutic plasma exchange (TPE), and immunoadsorption (IA), because only they have the ability to remove preformed or de novo developed antibodies quickly and effectively. The quick removal of antibodies and other plasma factors through TPE or IA remains an effective and supportive method for treating AMR and allows the TX despite preformed antibodies. The pertinent literature does not disclose, however, how often and for how long treatment should be administered. It is known, that repeated treatment cycles with adequately processed plasma volume must be used to overcome redistribution of pathological antibodies. Based on our experience in heart transplant recipients with compromised graft function due to non-HLA-ab and HLA-ab, IA seems to be more effective.

Exploring the role of cyclosporine in reducing homograft degeneration post-Ross

The Ross procedure is safe and effective for children with aortic valve disease. Pulmonary homograft degeneration, proposed to be immune-mediated, is a major cause of reoperation. Cyclosporine increased homograft valve survival in animals, but has not been studied in humans. To investigate the efficacy of low-dose cyclosporine in preventing homograft degeneration and complications, a retrospective historical-controlled study was performed on data of all children who underwent Ross procedure and received cyclosporine. The primary endpoint was homograft function at the last follow-up; secondary endpoints were readmission, reoperation, death, and safety. Seventeen patients were matched with 16 controls. At the end of the follow-up period (cyclosporine, 6.7 years; controls, 8 years), homograft stenosis and/or regurgitation were present in half of all patients. Three (18%) patients in the cyclosporine group and 5 (29%) in the control group were readmitted. Surgical intervention due to homograft failure was needed in 1 (6%) cyclosporine patient and 3 (19%) of the controls. Although cyclosporine failed to show a significant difference in signs of homograft degeneration, it might decrease the need for reoperation following the Ross procedure. Larger prospective well-designed studies are required to confirm these findings.

Role of T cells in graft rejection and transplantation tolerance

Transplantation is the most effective treatment for end-stage organ failure, but organ survival is limited by immune rejection and the side effects of immunosuppressive regimens. T cells are central to the process of transplant rejection through allorecognition of foreign antigens leading to their activation, and the orchestration of an effector response that results in organ damage. Long-term transplant acceptance in the absence of immunosuppressive therapy remains the ultimate goal in the field of transplantation and many studies are exploring potential therapies. One promising cellular therapy is the use of regulatory T cells to induce a state of donor-specific tolerance to the transplant. This article first discusses the role of T cells in transplant rejection, with a focus on the mechanisms of allorecognition and the alloresponse. This is followed by a detailed review of the current progress in the field of regulatory T-cell therapy in transplantation and the translation of this therapy to the clinical setting.

Antibody-Mediated Rejection of Cardiac Allografts in CCR5-Deficient Recipients

Rejected MHC-mismatched cardiac allografts in CCR5(-/-) recipients have low T cell infiltration, but intense deposition of C3d in the large vessels and capillaries of the graft, characteristics of Ab-mediated rejection. The roles of donor-specific Ab and CD4 and CD8 T cell responses in the rejection of complete MHC-mismatched heart grafts by CCR5(-/-) recipients were directly investigated. Wild-type C57BL/6 and B6.CCR5(-/-) (H-2(b)) recipients of A/J (H-2(a)) cardiac allografts had equivalent numbers of donor-reactive CD4 T cells producing IFN-gamma, whereas CD4 T cells producing IL-4 were increased in CCR5(-/-) recipients. Numbers of donor-reactive CD8 T cells producing IFN-gamma were reduced 60% in CCR5(-/-) recipients. Day 8 posttransplant serum titers of donor-specific Ab were 15- to 25-fold higher in CCR5(-/-) allograft recipients, and transfer of this serum provoked cardiac allograft rejection in RAG-1(-/-) recipients within 14 days, whereas transfer of either serum from wild-type recipients or immune serum from CCR5-deficient recipients diluted to titers observed in wild-type recipients did not mediate this rejection. Wild-type C57BL/6 and B6.CCR5(-/-) recipients rejected A/J cardiac grafts by day 11, whereas rejection was delayed (day 12-60, mean 21 days) in muMT(-/-)/CCR5(-/-) recipients. These results indicate that the donor-specific Ab produced in CCR5(-/-) heart allograft recipients is sufficient to directly mediate graft rejection, and the absence of recipient CCR5 expression has differential effects on the priming of alloreactive CD4 and CD8 T cells.

Role of Flow Cytometry to Define Unacceptable HLA Antigens in Lung Transplant Recipients with HLA-Specific Antibodies

BACKGROUND

Antidonor HLA-specific antibodies have been associated with hyperacute rejection and primary graft failure in lung transplant recipients. Thus, transplant candidates with HLA-specific antibodies generally undergo prospective crossmatching to exclude donors with unacceptable HLA antigens. However, the need to perform a prospective crossmatch limits the donor pool and is associated with increased waiting list times and mortality. A virtual crossmatch strategy using flow cytometry, which enables precise determination of HLA-specific antibody specificity, was compared to prospective crossmatching in sensitized lung transplant candidates.

METHODS

In all, 341 lung transplant recipients were analyzed retrospectively (April 1992 to July 2003). Sixteen patients with HLA-specific antibodies underwent transplantation based on flow cytometric determination of antibody specificity and 10 underwent prospective crossmatching.

RESULTS

Freedom from bronchiolitis obliterans syndrome (BOS) at three years was similar in those undergoing a virtual crossmatch, those undergoing prospective crossmatching, and those without HLA-specific antibodies (80.4% +/- 13.4, 85.7% +/- 13.2, and 73.8% +/- 2.8, respectively, P = 0.88). Three-year survival was also comparable (87.5% +/- 8.3, 70.0% +/- 14.5, and 78.5% +/- 2.4, respectively, P = 0.31). Elimination of prospective crossmatching for sensitized patients was associated with a significant decrease in time on the waiting list (P < 0.01) and in waiting list mortality (P < 0.05). All 16 patients undergoing a virtual crossmatch had negative retrospective crossmatches.

CONCLUSIONS

By carefully determining the specificity of HLA-specific antibodies, flow cytometry methodologies enable the prediction of negative crossmatch results with up to 100% accuracy, enabling the determination of appropriateness of donors. Using this virtual crossmatch strategy, crossmatching can be safely omitted prior to lung transplantation, thereby decreasing waiting list time and mortality rates for candidates with HLA-specific antibodies.

Acute Antibody-mediated Rejection of Cardiac Transplants

Under the direction of the International Society for Heart and Lung Transplantation, a multidisciplinary review of the cardiac biopsy grading system was undertaken in 2004, with task forces examining the areas of histopathology of rejection, clinical issues, and research. An important new area addressed by the Immunopathology Task Force sub-committee was the clinical and diagnostic criteria for antibody-mediated rejection. This article is a companion paper to the revised working formulation for the standardization of nomenclature in the diagnosis of heart rejection and reviews the published literature documenting the serologic and morphologic evidence that antibody-mediated rejection is clinically significant and associated with graft loss, accelerated transplant-associated coronary artery disease, and death. This article also provides a more in-depth analysis of antibody-mediated rejection developed by the Immunopathology Task Force for revision of the 1990 working formulation for the standardization of nomenclature in the diagnosis of heart rejection.

Two-year reduction of panel reactive human leukocyte antigen antibodies in children receiving mycophenolate mofetil after valved allograft placement

Allografts used in the repair of congenital heart defects in children induce a persistent broad HLA antibody response. We have previously shown that a 3-month course of mycophenolic mofetil (MMF) significantly reduces the HLA class I antibody response to valved allograft implantation in children. The purpose of this study was to determine if this reduction in HLA antibody persists after discontinuation of MMF. We conducted follow-up (mean 2 +/- 0.5 years) of seven patients who had received allograft placement for repair of congenital heart defects. These patients received 3 months of immunosuppression with MMF following allograft implantation. When compared to historical controls, patients who received MMF following surgery showed a significantly decreased HLA class I antibody response at 2 years postimplantation. This study demonstrates the ability to persistently alter the HLA class I antibody response using 3 months of MMF following allograft implantation in children.

Factors influencing late allograft valve failure

Allograft valves are a valuable valve replacement substitute in the surgical management of heart valve disease. It remains the valve substitute of choice in the reconstruction of the right ventricular outflow tract in children with congenital heart disease and in the Ross procedure. However, its durability remains suboptimal, particularly in children. This article reviews the mechanisms and factors implicated in late allograft dysfunction, with a focus on the evidence for an immunological cause for allograft valve failure. Unravelling the mechanisms of allograft valve failure may allow modification of the allograft to improve its long-term durability.

Anti-HLA antibodies in heart transplantation

We have analyzed the relationship between the development of transplant-related coronary artery disease (TRCAD) and the following potential risk factors: (a). number of HLA mismatches between recipient and donor; (b). production of anti-HLA antibodies; (c). growth of lymphocytes infiltrating the graft; and (d). frequency of biopsy proven episodes of acute rejection. The study population consisted of 285 adult heart allograft recipients who were monitored over a period of two years or more. The results demonstrate a significant correlation between TRCAD, generation of anti-HLA class II antibodies and potential of lymphocytes infiltrating the graft to proliferate ex-vivo in medium containing IL-2. Humoral and cellular immune responses to HLA-DR antigens expressed by the graft seem to underlie the development of TRCAD.

Anti-HLA antibody analysis and crossmatching in heart and lung transplantation

Although the clinical significance of anti-HLA antibodies in heart and lung transplantation is less well studied than in renal transplantation, several studies have shown that heart and lung recipients transplanted in the presence of donor-specific antibodies are at increased risk for early acute rejection and have a lower graft survival. In an effort to avoid any increase in organ ischemia time, heart and lung candidates with anti-HLA antibodies have to be identified prior to transplantation and crossmatches performed with donor materials obtained prior to organ recovery. Both class I and II antibodies have been found to be associated with chronic rejection, defined in heart transplantation as transplant-related coronary artery disease (TRCAV) and in lung transplantation as obliterative bronchiolitis (OB) or bronchiolitis obliterative syndrome (BOS). Post-transplant de novo development of donor antigen-specific class II antibodies has been found to be especially deleterious, significantly increasing the risk of chronic rejection and poor graft outcome. Based on the review of studies regarding the development of anti-HLA antibodies and thoracic organ allograft rejection several conclusions can be drawn. The presence of class I and II-directed anti-HLA antibodies, detected by any method, are associated with acute and chronic rejection in heart and lung transplantation. Different therapeutic strategies have been used pre-transplantation to decrease the level of anti-HLA antibodies and post-transplantation to maintain low antibody levels or treat rejection, thereby improving graft outcome. Thus, monitoring the presence and the level of anti-HLA antibodies is prognostic of graft outcome and allows for measurement of therapeutic efficacy.

Allograft Aortic Valve Replacement in the Adult: A Review

Aortic valve replacement using an allograft has been used continuously for over 40 years. Its advantages are excellent haemodynamic function, low thrombogenicity, resistance to infection and avoidance of the complications of anticoagulation. The main concern is its long-term durability, with the high hazard phase for failure between 10 and 20 years. We have only recently been able to judge the true long-term behaviour of the contemporary allograft with two recently published series of patients having reached follow-up beyond 20 years in significant numbers. This review of allograft aortic valve replacement in the adult covers the areas of history, benefits, techniques of sterilisation and preservation, operative methods and outcomes.

Significant changes in the alloantibody after lung transplantation in the cyclosporine treated rat model

BACKGROUND

The diagnosis of acute rejection after organ transplantation is often complicated by other possibilities, such as infection. Despite many attempts to identify rejection episodes after transplantation, only the detection of the humoral anti-human leukocyte antigen antibody has been effective in measuring alloimmunization, especially detected with flow cytometry cross-match (FCXM). As an initial step towards gaining a better understanding of the correlation between humoral responses and graft rejection in an immunosuppressant recipient, we investigated responses of alloantibodies (allo-Abs) after lung transplantation (LTx) in a rat model treated with adequate or inadequate cyclosporine A (CsA) therapy.

METHODS

Orthotopic LTx was performed using a major histocompatibility complex fully incompatible combination (Brown Norway to Lewis rat). CsA was given subcutaneously to recipients at an optimal or a sub-optimal dosage for 3 days after transplantation. A FCXM technique was used to determine the time-course of changes in titers of allo-Abs in serum. The allo-Ab deposition in the grafted lung was detected with an immunofluorescent staining method.

RESULTS

Circulating IgM allo-Ab levels were significantly elevated on day 4 in both groups when histological findings revealed early stage of acute rejection. IgM levels in the sub-optimal dosage group were maximal and significantly higher than those in the optimal dosage group on day 4, and levels then decreased after day 8. IgG allo-Ab levels increased significantly on day 8 and continued to increase throughout the observation period.

CONCLUSIONS

Our data suggest that the monitoring IgM allo-Abs might be effective for identifying acute rejection in recipients with inadequate immunosuppression therapy.

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

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

Immunogenicity of decellularized cryopreserved allografts in pediatric cardiac surgery: comparison with standard cryopreserved allografts

BACKGROUND

Recognition of the immunogenicity of standard cryopreserved allografts has led to the development of new decellularized allografts (CryoValve SG; CryoLife, Inc, Kennesaw, Ga). This preliminary study examined the HLA antibody response to these decellularized allografts and compared it with the response to standard allograft material.

METHODS

We prospectively measured the frequency of panel-reactive HLA class I (HLA-A, HLA-B, and HLA-C) and class II (HLA-DR/DQ) alloantibodies in 14 children (age 8.5 +/- 7.9 years) receiving decellularized, cryopreserved allografts, including 6 undergoing allograft patch insertion and 8 with a valved pulmonary allograft. We compared them with 20 historical control subjects (age 1.7 +/- 2.4 years) undergoing implantation of standard cryopreserved allografts, 8 with valves and 12 with allograft patch. All patients had panel-reactive antibody levels measured before and at 1, 3, and 12 months after the operation. HLA class I and class II panel-reactive antibody levels were determined with a sensitive flow cytometry technique.

RESULTS

We found panel-reactive antibody levels in decellularized allografts to be elevated slightly from preoperative levels for both class I and class II antibodies at 1, 3, and 12 months (P >.05). The panel-reactive antibody level for both class I and class II antibodies were significantly lower for decellularized allografts as compared to standard allografts. Functionally, the allografts were similar with decellularized valved grafts showing a peak echo-determined systolic gradient of 13 +/- 15 mm Hg at 8 +/- 2.6 months postoperatively as compared to a gradient of 24 +/- 18 mm Hg measured 12 +/- 6 months postoperatively in standard allografts (P =.11).

CONCLUSIONS

Decellularized grafts elicited significantly lower levels of class I and class II HLA antibody formation at 1, 3, and 12 months after implantation than did standard cryopreserved allografts. Early hemodynamic function of decellularized grafts was similar to that of standard cryopreserved allograft valves. Further experience is necessary to determine whether the reduced immunogenicity of decellularized allografts will truly allow tissue ingrowth and improved long-term durability in patients.

Humoral theory of transplantation

According to the humoral theory of transplantation, antibodies cause allograft rejection. Publications are cited showing that antibodies: (1). cause hyperacute kidney rejection, (2). lead to C4d deposits associated with early kidney graft failures, (3). are a good indicator of presensitization leading to early acute rejections, (4). were present in 96% of 826 patients who rejected a kidney graft, (5). are associated with chronic rejection in 33 studies of kidney, heart, lung and liver grafts, and (6). in three studies, appeared in the circulation BEFORE evidence of bronchiolitis obliterans in lung transplants, and BEFORE kidney rejection. In addition, a prospective cooperative study of 1629 patients in 24 centers demonstrated that antibodies foretold subsequent failures after a follow-up period of 6 months (p = 0.05). The specificity of antibodies detected in the serum of rejecting patients were often not donor specific, presumably because they were absorbed by the rejecting organ. If the humoral theory is accepted, even provisionally, transplanted patients who have antibodies could be treated with immunosuppression until the antibodies disappear to determine whether chronic rejection can be blocked. If successful, in patients who do not have antibodies, immunosuppression could be reduced until antibodies appear.

Formation of donor-specific human leukocyte antigen antibodies after kidney transplantation: correlation with acute rejection and tapering of immunosuppression

BACKGROUND

Before kidney transplantation, a serological crossmatch is routinely performed between donor and recipient to prevent hyperacute rejection by donor-specific anti-human leukocyte antigen (HLA) antibodies. After transplantation, the presence of these antibodies is not routinely monitored. We wanted to know whether donor-specific anti-HLA antibodies are detectable during acute rejection (AR), before or after reduction of immunosuppression in kidney transplant recipients who were converted from cyclosporine A (CsA) to the less nephrotoxic azathioprine (AZA) or mycophenolate mofetil (MMF) at 1 year after transplantation.

METHODS

Plasma samples were collected before transplantation, at several time points after transplantation, and during AR. Antibodies were measured in 29 patients: 5 patients with AR during the first year after transplantation (before conversion), 14 patients with AR after conversion or dose-reduction of AZA or MMF, and a control group of 10 patients without AR during a follow-up of 2 years (1 year before and 1 year after conversion of immunosuppression). Antibodies were measured by complement-dependent cytotoxicity assay, enzyme-linked immunosorbent assay (ELISA), and flow-cytometry in a crossmatch with donor spleen cells.

RESULTS

Donor-specific antibodies were not detectable after transplantation in the control group without AR, nor in patients with AR shortly after transplantation during CsA therapy. After conversion from CsA to AZA or MMF, antibodies appeared only in one patient after graft failure followed by transplantectomy and in patients during AR on AZA but not on MMF therapy.

CONCLUSION

In this patient group, we could not detect donor-specific antibodies during CsA treatment, not even at the time of AR using three different techniques. Donor-specific antibodies were primarily present during AR in patients converted from CsA to AZA and were not found in the sera from patients converted to MMF.

Specialized transfusion support for solid organ transplantation

As solid organ transplantation becomes increasingly common and complex, the demands on the transfusion service expand. Transplant recipients present unique challenges not only because of product availability but also because of specialized blood components, serologic problems, and immunologic effects of transfusion on the allograft and the recipient. Solid organ transplant recipients receive immunosuppressive agents that make them more susceptible to infectious or immunologic complications of transfusion such as cytomegalovirus infection and graft-versus-host disease. Other immunologic consequences of transfusion such as alloimmunization may also be severe, resulting in acute or chronic graft rejection. The transfusion specialist must recommend the optimal approach to reducing the risk of these complications in organ transplant recipients.

HLA-antibody testing: the immune phagocytosis inhibition test is superior to the PRA-STAT and NIH lymphocytotoxic test with respect to specificity

We compared the specificity and sensitivity of four different methods for the detection of antibodies specific for HLA antigens. The NIH version of the complement-dependent cytotoxic test (CDC) was used as the gold standard to which we compared two Fcgamma receptor (FcgammaR)-dependent immune phagocytosis inhibition tests (IPI) and one commercial enzyme-labelled immunosorbent assay (ELISA) with soluble HLA class I-antigen preparations bound to the plate (PRA-STAT). Both IPI tests are based on the fact that HLA-antibodies specifically bind to antigens on the monocyte surface via their Fab portion, and in so doing block a neighbouring FcgammaR with their Fc region. This blockade prevents phagocytosis of IgG-coated red blood cells (RBCs), which can be measured either microscopically (IPIm) or photometrically (IPIp). The four assays were used in blind tests on 20 human alloantisera or monoclonal antibodies with known HLA-antigen reactivities. Additionally, two monoclonal antibodies and one human serum were titrated to elucidate the sensitivity of each test. After all tests were completed, the identities of the samples were disclosed. Both IPI methods detected and identified all clinically relevant HLA class I and class II specific antibodies. In contrast, the CDC was not able to detect noncytotoxic HLA-antibodies and HLA class II specific antibodies; however, it detected clinically insignificant IgM lymphocytotoxins. The PRA-STAT assay enabled identification of all cytotoxic and noncytotoxic IgG antibodies with specificity for HLA-class I antigens. With respect to sensitivity, the CDC and the IPI methods were superior to the PRA-STAT. These facts demonstrate the advantage of IPI methods in the detection of clinically relevant HLA-antibodies.

Identification of ICAM-1 polymorphism that is associated with protection from transplant associated vasculopathy after cardiac transplantation

Transplant associated coronary disease (TxCAD) is the main cause of late graft loss following cardiac transplantation. It is a multifactorial disease with immunologic and nonimmunologic components involved. This study was undertaken to analyze the gene polymorphism in adhesion molecules in donors and recipients and to investigate its potential association with the development of TxCAD. A total of 82 cardiac transplant patients, 96 donors and 101 UK controls, were genotyped retrospectively. Nine nucleotide polymorphisms in L-selectin, E-selectin, ICAM-1, and PECAM were analyzed using allele-specific PCR-SSP assay. Recipients were selected on the basis of the development of TxCAD: patients who had developed TxCAD within 2 years after transplantation, and patients who did not have TxCAD within 4.5-5 years after transplantation. All recipients received CyA and azathioprine as a primary immunosuppression. Associations were assessed by using Fisher's exact test. No association was found between E-selectin, L-selectin, and PECAM allele or genotype frequencies and TxCAD. However, the donors whose recipients did not develop TxCAD at first 2 years had a significant increase of ICAM-1 E-469 allele compared with donors, whose recipients developed TxCAD (63.8% vs 46.4%, p = 0.042) and to UK controls (63.8% vs 47%, p = 0.04). Moreover, we found that the decreased frequency of ICAM E469 allele was associated with the increased number of rejection episodes. The 469 E/K polymorphism is in exon 6 and results in a change from glutamic acid to lysine in Ig-like domain 5 of ICAM-1, which is thought to affect interactions with LFA-1 and adhesion of B-cells. Our data suggest the presence of allele E469 ICAM-1 in either donor or recipient is protective against allograft rejection in a transplant setting.

A Prospective Analysis of the Immunogenicity of Cryopreserved Nonvalved Allografts Used in Pediatric Heart Surgery

Background —The purpose of this study was to prospectively determine the immunogenicity of nonvalved allograft tissue used to repair congenital heart defects.

Methods and Results —We prospectively analyzed the immune response of 11 children, 1.4 months to 10 years of age, who required nonvalved allografts to alleviate stenosis during repair of congenital heart defects. In 7 patients, pulmonary arterial grafts were used; in 3 patients, monocusp pulmonary artery grafts were used; and in 1 patient, a section of glutaraldehyde-preserved allograft pericardium was used. We measured the level of HLA panel-reactive antibody (PRA) before surgery, 1 week after, 1 month after, and 3 months after surgery. PRA was determined by the antiglobulin technique and flow cytometry. HLA class I and class II antibodies measured by either technique were negligible before and 1 week after surgery. Nine of 11 patients (82%) exhibited a significant immune response at 1 month after surgery that further increased at 3 months. The measured PRA for class I antibodies with the antiglobulin technique increased to 43±36% at 1 month and to 69±38% at 3 months after surgery. Flow cytometry class I PRA measurements were similar. Class II PRA increased to 26±34% at 1 month and to 41±36% at 3 months. Age negatively correlated with the degree of elevation of PRA, but neither allograft area nor the area indexed to patient body surface area correlated with PRA.

Conclusions —Cryopreserved nonvalved allografts induce a strong HLA antibody response in the majority of children.

Cardiac allograft vasculopathy

Cardiac transplantation has emerged as a valuable therapy for various end-stage cardiac disorders. Cardiac allograft vasculopathy (CAV), an unusually accelerated and diffuse form of obliterative coronary arteriosclerosis, determines long-term function of the transplanted heart. Cardiac allograft vasculopathy is a complicated interplay between immunologic and nonimmunologic factors resulting in repetitive vascular injury and a localized sustained inflammatory response. Dyslipidemia, oxidant stress, immunosuppressive drugs, and viral infection appear to be important contributors to disease development. Endothelial dysfunction is an early feature of CAV and progresses over time after transplantation. Early identification of CAV is essential if long-term prognosis is to be improved. Annual coronary angiography is performed for diagnostic and surveillance purposes. Intravascular ultrasound is a more sensitive diagnostic tool for early disease stages and has revealed that progressive luminal narrowing in CAV is in part due to negative vascular remodeling. Because of the diffuse nature of CAV, percutaneous and surgical revascularization procedures have a limited role. Prevention of CAV progression is a primary therapeutic goal.

Specific B cell tolerance is induced by cyclosporin A plus donor-specific blood transfusion pretreatment: prolonged survival of MHC class I disparate cardiac allografts

Donor-specific blood transfusion (DST), designed to prolong allograft survival, sensitized recipients of the high-responder PVG-RT1u strain, resulting in accelerated rejection of MHC-class I mismatched (PVG-R8) allografts. Rejection was found to be mediated by anti-MHC class I (Aa) alloantibody. By pretreating recipients 4 wk before grafting with cyclosporin A (CsA) daily (x7), combined with once weekly (x4) DST, rejection was prevented. The investigation explores the mechanism for this induced unresponsiveness. CD4 T cells purified from the thoracic duct of CsA/DST-pretreated RT1u rats induced rejection when transferred to R8 heart-grafted RT1u athymic nude recipients, indicating that CD4 T cells were not tolerized by the pretreatment. To determine whether B cells were affected, nude recipients were pretreated, in the absence of T cells, with CsA/DST (or CsA/third party blood) 4 wk before grafting. The subsequent transfer of normal CD4 T cells induced acute rejection of R8 cardiac allografts in third party- but not DST-pretreated recipients; prolonged allograft survival was reversed by the cotransfer of B cells with the CD4 T cells. Graft survival correlated with reduced production of anti-MHC class I (Aa) cytotoxic alloantibody. The results indicated that the combined pretransplant treatment of CsA and DST induced tolerance in allospecific B cells independently of T cells. The resulting suppression of allospecific cytotoxic Ab correlated with the survival of MHC class I mismatched allografts. The induction of B cell tolerance by CsA has important implications for clinical transplantation.

Anti-HLA antibodies after solid organ transplantation

We have cited more than 23 studies showing that de novo development of anti-HLA antibodies is associated with increased acute and chronic rejection and decreased graft survival in kidney, heart, lung, liver, and corneal transplants. Antibodies to both HLA class I and class II antigens seem to be detrimental. Antibodies of the IgG isotype and possibly the IgM isotype were clinically relevant. Most studies showed that donor-specific antibodies were associated with rejection and graft loss. Therefore, HLA antibodies provide a clinical readout for patient alloreactivity that may have the ability to distinguish graft dysfunction due to immunologic and nonimmunologic causes. Antibody may act as a critical trigger for rejection of allografts and may serve as an early indicator of a slowly smoldering chronic rejection that is not manifested at a given time by biochemical measures such as serum creatinine levels. The effectiveness of various drugs on chronic rejection should be evaluable by their effects on HLA antibody production. We predict that recently developed ELISA and flow cytometry techniques using purified HLA antigen will increase the clinical relevance of posttransplantation HLA antibody monitoring by (1) allowing the detection of low levels of donor antibody; (2) easily distinguishing the isotype and target (HLA class I or class II) of the antibodies; and (3) correlating the antibody with specific graft pathology.

Class I and class II anti-HLA antibodies after implantation of cryopreserved allograft material in pediatric patients

OBJECTIVES

Very little is known regarding the immune response to cryopreserved allograft valves and patch material used in the surgical repair of congenital heart defects.

METHODS

We prospectively measured the frequency of panel reactive antibodies directed against HLA class I (HLA-A, B, and C) and class II (HLA-DR/DQ) alloantigens in 24 children receiving cryopreserved allografts. We compared them with results in 11 previously reported control patients. Sixteen of the study patients underwent placement of a valved conduit (11 pulmonic, 5 aortic) between the right ventricle and pulmonary arteries, 6 underwent patch angioplasty of stenotic vessels with cryopreserved pulmonary artery, and 2 underwent placement of a pulmonary monocusp patch. Study patients had panel reactive antibodies measured before, 1 month, 3 months, and 1 year after the operation.

RESULTS

With allograft implantation, panel reactive antibodies increased from 1.9% +/- 5% before the operation to 62% +/- 33% at 31 +/- 8 days after the operation, 92% +/- 15% at 3.3 +/- 0.6 months after the operation, and 85% +/- 18% at 1.1 +/- 0.2 years after the operation. The control group showed no change in panel reactive antibodies, with a level of 1.6% +/- 1% before the operation, 3.2% +/- 1% 28 +/- 5 days after the operation, and 1.7% +/- 1% 2.7 +/- 0.3 months after the operation. Class II antibodies (anti-HLA-DR/DQ) rose to 49% +/- 35% at 30 +/- 8 days and 70% +/- 26% at 3.3 +/- 0.6 months after the operation.

CONCLUSIONS

Cryopreserved allograft material induces a marked response that involves both class I and class II anti-HLA antibodies within 3 months after operation in children. This alloantibody response may represent a form of "rejection," may have implications for those who require subsequent cardiac transplantation, and may play a role in early allograft failure.

Coronary artery disease after heart transplantation and its relation to cytomegalovirus

The most common cause of death and retransplantation after heart transplantation is a rapidly progressive, obliterative vascular disease involving the coronary arteries, termed cardiac allograft vasculopathy (CAV). Most believe that this is a form of chronic rejection. Several clinical series have suggested an association between cytomegalovirus and CAV. Rat cytomegalovirus enhances the development of CAV in rat heterotopic heart or aortic transplantation models. The mechanism(s) by which cytomegalovirus might have an impact on the severity of chronic rejection include the augmentation of vascular growth factors, the alteration in the alloimmune response directly or the alteration of cytokines and cell adhesion molecules, enhancing cellular and humoral interactions. We previously reported that the infection of smooth muscle cells by cytomegalovirus resulted in the alteration of major histocompatibility complex class I molecules on the smooth muscle cell surface. In a subsequent report we demonstrated that a sublethal inoculum of cytomegalovirus produced no cytopathology in smooth muscle cells yet had the same viral burden as fibroblasts, which demonstrated cytopathology. The identical effects on major histocompatibility complex class I were observed in smooth muscle cells, and cytokine gene transcription was altered, favoring a proinflammatory milieu. These and most in vitro studies are carried out with the use of traditional laboratory strains of cytomegalovirus. We have subsequently demonstrated major genotypic differences between laboratory and clinical strains of cytomegalovirus that are associated in differences in biological activity in vitro. These include differences in tropism for vascular cells, differences in cell surface antigen expression, and differences in mesenchymal growth factor gene expression. All of these may have important implications with regard to associating cytomegalovirus with CAV.

Immune response following fresh arterial homograft replacement for aortoiliac graft infection

INTRODUCTION

this prospective study defines the immune response to fresh arterial homograft replacement for graft infection.

MATERIALS AND METHODS

ten patients who underwent ABO-compatible homograft transplantation were studied for anti-HLA antibody production, and CD3-CD4-CD8-positive lymphocytes subset. Immunological studies were performed preoperatively, and at early (1, 3, 7 days) and late (1, 3, 6, 12, 18, 24 months) follow-up. All patients received immunosuppressive treatment with cyclosporine (1-3 mg/kg/day). Abdominal CT scans were performed postoperatively at the 1, 6, 12, 18, 24 months follow-up.

RESULTS

preoperatively, antibodies could not be detected. Postoperatively, as from 1st month post-transplant, a progressive increase in % PRA was observed in all patients, up to the 12th month of follow-up. Subsequently, at 18 and 36 months, a progressive decrease in % PRA was detected. Data showed that the recipient antibodies were directed against donor-specific antigens. During the immediate postoperative period (1, 3, 7 days) CD3- and CD4-positive T lymphocytes slightly increased, whereas CD8 simultaneously decreased. Later, CD3 and CD4 progressively decreased and CD8 increased. Clinically, all patients were cured of infection at late follow-up. CT scans showed thickening of the aortic wall (range: 2.5-4.5 mm), with no signs of aneurysmal degeneration.

CONCLUSIONS

fresh arterial homografts are immunogenic. Implanted homografts induce a strong anti-HLA antibody response, similar to chronic rejection, in spite of immunosuppressive treatment.

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.

The significance of HLA matching in cardiac transplantation

It is argued that HLA matching is not worthwhile in heart transplantation. However, transplanting HLA compatible hearts enhances graft survival and should significantly reduce infection and malignancies related to aggressive immunosuppression. It is our view that the problem is technical and we offer a potential solution.

Effect of HLA mismatching and antibody status on "homovital" aortic valve homograft performance

BACKGROUND

Recipients of "homovital" aortic valve homografts are known to produce specific antibodies to human leukocyte antigen (HLA) determinants present on the cellular compartment of the valve tissue; however, the clinical significance of these antibodies is unknown. Data from 182 patients receiving homovital aortic valve homografts has been analyzed to determine the impact of HLA disparity and HLA antibody production on survival and function of the homograft.

METHODS

Human leukocyte antigen mismatch data were available for 127 patients (mean follow-up, 6.02+/-0.26 years). Two patients were considered well matched for HLA A+B antigens (zero or one mismatch) compared with 125 poorly matched (two to four mismatches). Nine patients had a zero HLA-DR mismatch compared with 52 with one mismatch and 59 patients completely mismatched for DR antigens.

RESULTS

There was no significant association between the degree of HLA mismatch for either class I or class II antigens whether the loci were considered alone or in combination (ie, A, B, DR, AB, or ABDR mismatching) with markers of long-term valve function including patient mortality, reoperation, valve degeneration, valve stenosis, presence of regurgitation, and postoperative New York Heart Association class. One hundred thirty-six of 167 (82%) were found to have produced antibodies after operation (mean time after operation, 6.42+/-0.58 years). In 61 cases both antibody specificity and donor HLA typing was available. In 92% of these, the antibodies were of the IgG subclass and were specific for the HLA class I molecules of the donor. The presence of HLA antibodies was associated with an increase in the frequency of mild valve stenosis (not significant) compared with those patients who did not develop HLA antibodies (antibody negative = 9.7%; panel reactive antibodies <50% = 29.1%; and panel reactive antibodies >50% = 22.2%; not significant). There was also an increased prevalence of valve degeneration associated with HLA antibodies. The actuarial freedom from valve degeneration for the 35 HLA antibody-negative patients was 100% at 1, 5, and 10 years compared with 100% at 1 year, 97% at 5 years, and 92% at 10 years for 55 patients with panel reactivity less than 50%, and 98% at 1 year, 94% at 5 years, and 88% at 10 years for the 77 patients who were highly sensitized (not significant). There was no correlation with other markers of long-term valve function.

CONCLUSIONS

The influence of the immune response on valve function requires further studies involving large numbers of patients followed for a longer period of time. We believe prospective matching for HLA antigens is warranted to produce a well-matched cohort of patients for analysis and to reduce antibody sensitization, which would help to clarify this issue.

Endothelial cell activation by sera containing HLA antibodies is mediated by interleukin-1

BACKGROUND

It has been suggested that antibodies which are associated with chronic pathological conditions such as chronic rejection and autoimmune diseases have the capacity to activate endothelial cells by induction and up-regulation of adhesion molecules. It has also been suggested that HLA antibodies formed by patients awaiting transplantation can activate endothelial cells. These antibodies include HLA and those that bind to endothelial cells.

METHODS

We have further investigated this phenomenon using monoclonal antibodies against HLA class I determinants and sera from aortic valve graft recipients, containing strong HLA antibodies. The effect of 24-hr incubation of antibodies/serum with human umbilical vein endothelial cells (HUVECs) on adhesion molecule expression was measured by flow cytometry.

RESULTS

HLA monoclonal antibodies had no effect on ICAM-1 expression on HUVECs. Five of 31 (16%) patients' sera caused strong up-regulation of adhesion molecules (ICAM-1, vascular cell adhesion molecule-1, and E-selectin) but this did not correlate with HLA specificity, IgG, or IgM binding to HUVECs. The activity, found in whole serum and IgG-depleted fractions was inhibited by neutralizing antibodies against interleukin (IL)-1beta and tumor necrosis factor-alpha. Examination of patient sera for presence of IL-1beta demonstrated high levels of IL-1beta in all five sera (range, 30 -500 U/ml) as well as in samples from an additional three patients.

CONCLUSION

The ability to activate endothelial cells detected in our patient sera was caused by cytokines and not antibody. Our observation that addition of cytokines to sera before separation into large and low molecular weight fractions demonstrated retention of cytokines in both fractions may be a confounding issue when investigating endothelial cell activation by patients' sera.

Contrasting outcomes of donor-specific blood transfusion: effectiveness against cell-mediated but not antibody-mediated rejection

BACKGROUND

Giving recipients a prior donor-specific blood transfusion (DST) is effective in prolonging organ allograft survival in some inbred strains but not in others. The present investigation analyzed two such contrasting strains of rats in an attempt to define the basis for this variation.

METHODS AND RESULTS

The survival of fully mismatched Dark Agouti (RT1a) cardiac allografts was significantly prolonged (from 7 to 44 days, median survival times) in PVG (RT1c) rats given a prior (-14 day) DST, whereas it shortened survival in the high-responder PVG-RT1u strain. Injecting PVG recipients with blood from strains bearing defined differences indicated that each disparity contributed to the increased survival time in an incremental way: blood and heart matched at the MHC class I (A) and/or class II (B/D) loci had a major influence on survival; class I-like (C) and non-MHC antigens made only minor contributions. MHC disparities had contrasting effects in RT1u rats. Blood transfusions from Dark Agouti or PVG-R8 (AaB/DuCu) rats induced accelerated rejection and anti-Aa alloantibody formation; transfusing PVG-R23 (AuB/DaCa) blood, a class II and class I-like difference, induced indefinite R23 heart allograft survival. Although produced in high titer, anti-class II antibody was not able to induce rejection in RT1u rats. Specific anti-Aa alloantibody was able, after passive transfer, to destroy class I-disparate allografts in both RT1u nude and PVG nude recipients. However, under normal circumstances, acute rejection in the PVG strain occurred in the absence of anti-Aa antibodies, presumably by a cell-mediated mechanism.

CONCLUSION

Anti-class I alloantibody, when produced, seemed to override the unresponsiveness induced by DST. The results indicated that DST was effective only when rejection was induced by a cell-mediated response. The two contrasting response patterns in animals may reflect the experience of transplant patients who either benefit from DST or become sensitized instead.

An immunological algorithm to predict risk of high-grade rejection in cardiac transplant recipients

BACKGROUND

Transplant-related coronary-artery disease (TCAD) develops frequently in cardiac-allograft recipients, and limits long-term survival. We examined the relation between this disorder and cumulative frequency of high-grade rejection, and investigated whether concomitant use of three immunological factors at the time of a low-grade endomyocardial biopsy can predict progression to high-grade rejection.

METHODS

We investigated the relation between the cumulative annual frequency of high-grade rejection and TCAD in 198 recipients of cardiac transplantation between 1992 and 1996 by means of Kaplan-Meier actuarial life-tables. Endomyocardial biopsy, lymphocyte-growth assays, and anti-HLA antibody measurements were compiled over 12 months in 102 patients during their first post-transplant year. We calculated predictive values for high-grade rejection within 90 days by chi2, Kaplan Meier survival curves, and by multivariable logistic regression analyses.

FINDINGS

We found a direct correlation between cumulative annual frequency of rejection and TCAD onset with highest risk in those with more than 0.75 rejections per year (p=0.0002). After a low-grade endomyocardial biopsy (0 or 1A), one or more donor-recipient HLA-DR matches protected against high-grade rejections (p<0.001). Among individuals with one or two DR matches, the negative predictive value for progression from a low-grade biopsy to a high-grade rejection was 87% in the presence of a negative lymphocyte-growth assay. Among individuals with no DR matches, the presence of either a positive lymphocyte-growth assay or IgG anti-major-histocompatibility complex (MHC) class II antibodies was independently associated with high probability of progression to rejection (64% and 66%, respectively, p<0.0005). When both assays were positive, concomitantly with a low-grade endomyocardial biopsy, the positive predictive value for progression to a high-grade rejection was 86% (p<0.0001). For endomyocardial-biopsy grades 1B or 2, a positive lymphocyte-growth assay alone was associated with high-grade rejection in 100% of cases.

INTERPRETATION

Use of an algorithm combining three immunological factors at the time of a low-grade endomyocardial biopsy enables prospective stratification of cardiac transplant recipients into risk categories for progression to high-grade rejection. Low-risk individuals require fewer biopsies, moderate-risk individuals require an ongoing schedule of surveillance biopsies, and high-risk individuals require rational organisation of interventional strategies aimed at preventing rejection. Additional predictive factors are needed to identify moderate-risk individuals who will progress to rejection. Ultimately, successful intervention may have an impact on the subsequent complication of TCAD.

A new enzyme-linked immunosorbent assay to measure anti-endothelial antibodies after cardiac transplantation demonstrates greater inhibition of antibody formation by tacrolimus compared with cyclosporine

BACKGROUND

Chronic rejection or transplant-associated coronary artery disease (TxCAD) is the most serious complication after human cardiac transplantation. Previous studies, using Western blotting, have shown formation of antibodies against endothelial antigens of 56 and 58 kDa, which are associated with early TxCAD. These antigens were later identified as being vimentin and its breakdown products. The aims of the present study were to devise a robust assay for detection of anti-vimentin antibodies and to compare antibody formation in patients taking different immunosuppressive drugs.

METHODS

106 sequential serum samples from 19 patients taking tacrolimus and 68 sera from 12 patients taking cyclosporine were examined by enzyme-linked immunosorbent assay (ELISA) for anti-vimentin antibodies and Western blotting for reactivity against bands at 56/58 kDa. Serum samples were taken before transplantation and at 1, 3, 6, 9, and 12 months.

RESULTS

The vimentin ELISA produced significantly higher numbers of positive episodes per patient (3.92+/-1.08) compared with use of Western blotting (2.54+/-0.52). Serum from patients taking tacrolimus contained significantly less antibodies measured by ELISA (15.8%) or Western blotting (6.5%) than sera from patients taking cyclosporine (46.8% for ELISA; P=0.001 and 21% by Western blotting, P=0.01). Intravascular ultrasound performed on six patients at 12 months showed a correlation between anti-vimentin antibody formation and detection of early coronary disease.

CONCLUSIONS

The results demonstrate first, that differences in antibody profiles produced by different immunosuppressive drugs, and second, that detection of anti-vimentin antibodies may be a noninvasive method of detecting disease activity in transplanted vessels.

Cardiac allograft rejection late after transplantation is a risk factor for graft coronary artery disease

BACKGROUND

Graft coronary artery disease (CAD) is an increasingly important problem during long-term survival after heart transplantation, but the importance of cellular rejection, in particular late after transplantation, remains undetermined.

METHODS AND RESULTS

We analyzed 492 coronary angiographies (967+/-705 days after transplantation; range, 49 days to 9.4 years) and 5201 endomyocardial biopsies (518+/-648 days after transplantation) from 156 patients (age, 47+/-11 years). Patients with angiographically detectable graft CAD had significantly more episodes of rejection requiring augmentation of immunosuppressive therapy (i.e., International Society of Heart and Lung Transplantation score > or = 3A) than those without graft CAD during the first (3.7+/-2.6 vs. 2.2+/-2.0, P<0.001) as well as subsequent years after transplantation (1.2+/-1.9 vs. 0.4+/-0.9, P<0.01). Multivariate logistic regression analysis including established risk factors for CAD, ischemic time, gender and age of donors and recipients, number of mismatches, cytomegalovirus infection, and drug therapy showed that the number of rejections during the first [odds ratio (OR)=1.39, P<0.005] as well as subsequent years (OR=1.49, P<0.05), previous cytomegalovirus infection (OR=3.21, P<0.05), donor age >40 years (OR=2.97, P<0.05), and current or former smoker status (OR=2.76, P<0.05) were independent predictors of graft CAD. In patients without angiographically detectable graft CAD 1 year after transplantation, the number of rejections after the first year was even more strongly related to graft coronary artery disease than in the total patient population, underlining the importance of late cellular rejection (OR=1.74, P<0.005).

CONCLUSION

Rejection requiring augmentation of immunosuppression early and late after transplantation is an independent risk factor for the development of angiographically detectable graft CAD. Hence, the search for and treatment of moderate or severe rejection seems to be prudent even late after transplantation.

Detection of HLA-specific antibodies by PRA-STAT and their association with transplant outcome

OBJECTIVE

The aim was to investigate the correlation between renal transplant outcome and the presence of HLA-specific antibodies detected using the ELISA kit PRA-STAT as compared with complement-dependent cytotoxicity (CDC).

METHOD

295 sera from 95 renal transplant recipients (99 transplants) were investigated for the presence of HLA-specific antibodies using both PRA-STAT and CDC. The patients were divided into group I (49 transplants failed within 1 month) and group II (50 successful transplants).

RESULTS

The concordance between PRA-STAT and CDC for the detection of HLA class I-specific antibodies was 87.8% (259 of 295). For 19 sera, antibodies were detected only by PRA-STAT; for 17 sera, antibodies were detected only by CDC. No donor-specific antibodies were detected by either technique for patients in group II. For four group I patients (six sera), donor-specific IgG antibodies were detected only by PRA-STAT (one before, three after transplant) and all four transplants failed. For five other group I patients (six sera), donor HLA-specific antibodies were detected only by CDC (one before, four after transplant) and all five transplants failed. The antibodies detected before transplant by CDC were shown to be IgM alloantibodies.

CONCLUSION

This study showed that PRA-STAT could detect HLA-specific IgG antibodies relevant to transplant outcome that were not detected by CDC. However, it could not detect IgM alloantibodies that were also shown to be important. PRA-STAT is therefore a useful addition to a histocompatibility laboratory's screening repertoire only when used in conjunction with other techniques.

Cardiac allograft vasculopathy: IgM antibody responses to donor-specific vascular endothelium

We have previously demonstrated that heightened cell-mediated immunity to donor-specific endothelium was associated with an increased incidence of cardiac allograft vasculopathy (CAV) at 1 year postcardiac transplantation. We further demonstrated that the development of IgG antibody directed to donor-specific HLA antigens was extremely uncommon and, furthermore, had no relationship to the development of CAV. Subsequent studies have demonstrated a correlation between IgM antibody directed against endothelial cell antigens and the development of CAV. Accordingly, recipient serum obtained between 6 and 8 weeks (early) and 1 year (late) after transplantation were reacted with recombinant human interferon (rhIFN)-gamma pretreated donor-specific human aortic endothelial cells (HAECs) in 10 recipients with and 10 recipients without CAV at 1 year after transplantation. HAEC IgM binding was assessed by flow cytometry and complement fixation and HAEC lysis was measured using standard chromium release assays. Seven of 10 and 5 of 10 patients with CAV had IgM detected by flow at early and late time points, respectively (14+/-2 and 16+/-5 mean channel shift), whereas 5 of 10 and 6 of 10 patients without CAV had IgM detected by flow at early and late time points, respectively (15+/-4 and 14+/-3 mean channel shift). This finding was not different between groups. Despite between 50% and 70% of all patients having detectable IgM binding to ECs, no patient's serum was cytotoxic to its donor-specific HAECs. We conclude that IgM antibody to endothelial cells is common (at low titers) after transplantation. This antibody is not cytotoxic and in this study provided no discrimination between those with and without chronic rejection.

Anti-cell surface endothelial antibodies in sera from cardiac and kidney transplant recipients: association with chronic rejection

The aetiologies of accelerated or transplant-associated coronary artery disease (TxCAD) following cardiac transplantation and chronic rejection following renal transplantation remain ill-defined. Previous studies have used Western blotting to demonstrate an association between the formation of anti-endothelial (anti-EC) antibodies and TxCAD after heart transplantation. However, Western blotting favours detection of cytosolic proteins. The objectives of this study were to determine whether flow cytometry, a method which detects antigens on the cell surface, could be used to detect anti-EC antibodies and also whether the observations would extend to renal transplant patients with chronic rejection. Flow cytometry was used to look for antibodies reactive with the surface antigens of macrovascular and microvascular endothelial cell lines in sera from 44 cardiac and 35 renal transplant recipients before and after transplantation. In addition, sera from normals (n = 20), patients with nontransplant CAD (n = 50) and patients with unrelated diseases (n = 40) were investigated. Of 23 cardiac recipients who had developed TxCAD at one or two years post-transplant, 61% had IgM and 13% had IgG anti-EC antibodies post-transplantation. In contrast, in 21 cardiac recipients who had not developed TxCAD 14% had IgM and 14% IgG anti-EC antibodies. There was little evidence for the presence of anti-EC antibodies in cardiac recipients before transplantation. Of 26 renal transplant recipients whose transplants failed due to chronic rejection, 42% had IgG and 19% IgM anti-EC antibodies post-transplantation. Of nine renal recipients whose grafts were either functioning normally or who had acutely rejected, none had IgG or IgM anti-EC antibodies either pre- or post-transplantation. The anti-EC antibodies were not found in normals and were rare (less than 4%) in the other disease groups; they do not appear to be autoantibodies. In conclusion, these results suggest the FACS assay could be an informative and rapid test to provide more information on chronic rejection following cardiac and renal transplantation.

Identification of patients at high risk of graft loss by pre- and posttransplant monitoring of anti-HLA class I IgG antibodies by enzyme-linked immunosorbent assay

Identification of risk factors influencing graft survival may lead to the development of models to predict graft outcome. Such models may provide guidance for immunosuppressive therapy, measure posttransplantation outcome, and eventually improve graft survival in high-risk patients. A major risk factor influencing graft survival is allosensitization. However, due to the lack of standardization of lymphocytotoxicity assays, the detection of alloantibodies utilizing this current methodology may not correlate with posttransplant events. Recently, a novel standardized enzyme-linked immunosorbent assay (ELISA) for the detection of anti-HLA class I IgG antibodies was developed. To evaluate the predictive value of this diagnostic test, a retrospective analysis of 124 renal allograft recipients with an 18-month follow-up time was performed. A highly significant (P=0.01) correlation between pre-transplant ELISA panel reactive antibody (PRA) results and graft loss was observed. Patients with pre-transplant ELISA PRA of >10% had a three times higher risk of graft loss compared with patients who tested negative. No such correlation was observed with complement-dependent cytotoxicity results independent of the reduction of IgM antibodies with dithiothreitol. Similarly, a highly significant correlation of ELISA results with the occurrence of early graft dysfunction was observed. Almost all patients (88%) with a pretransplant ELISA PRA of >50% required posttransplant dialysis, compared with 45% of patients with a pretransplant ELISA PRA of 10-50% and 27% of patients with a pretransplant ELISA PRA of <10%. No such difference was observed with complement-dependent cytotoxicity %PRA values. Analysis of posttransplant specimens by ELISA demonstrated a strong correlation of assay results with graft rejection and graft dysfunction. In summary, these results suggest that detection of anti-HLA class I antibodies by ELISA identifies patients at high risk for graft loss. No other single risk factor of such magnitude has been identified so far.