Histocompatibility in cardiac transplantation with particular reference to immunopathology of positive serologic crossmatch

How to deal with presensitized candidates for heart transplantation?

PURPOSE OF REVIEW

With increasing utilization of assist devices and adoption of calculated panel-reactive antibody (cPRA), the number of presensitized patients being listed for heart transplantation is increasing. An effort to standardize identification and management of such patients is paramount and recently initiated in the heart transplant community. The current review describes the basic concepts of presensitization and details the most relevant work including the latest advancements in this area.

RECENT FINDINGS

More sensitive techniques in identifying presensitized patients have posed challenges in understanding the clinical relevance and implications of such testing. cPRA has been shown to benefit presensitized heart transplant patients. De-sensitization strategies have never been studied in a large clinical trial setting but a combination of plasmapheresis and intravenous immunoglobulin has been shown to be beneficial in small studies. Long-term positive outcomes of de-sensitization have been recently reported. Newer agents like alemtuzumab, bortezomib and complement inhibitors have been reported in case reports and series with promising results as de-sensitization strategy.

SUMMARY

Data specific to strategies and therapies in heart transplantation are sparse and most knowledge stems from other organ transplantation. Consensus efforts to standardize care and also advance research in this area were initiated recently with hope for improving care for these patients.

Experience with bovine pericardium for the reconstruction of the aortic arch in patients undergoing a Norwood procedure

BACKGROUND

The incidence of recurrent aortic arch obstruction after the Norwood procedure is between 0% and 36%. Allograft material is frequently used to enlarge the aorta; its use has been associated with the development of significant allosensitization. We report our experience using bovine pericardium for the reconstruction of the aortic arch in patients undergoing a Norwood procedure.

METHODS

A retrospective analysis of 33 consecutive patients evaluated for a second-stage procedure after an initial Norwood repair was performed. All patients underwent a cardiac catheterization. The presence of recurrent arch obstruction (gradient > 10 mm Hg) and its management were noted. Three consecutive patients were tested for anti-HLA antibodies at the time of their Fontan procedure.

RESULTS

The mean age at the time of the cardiac catheterization was 4.12 months (range, 2 to 7 months). The incidence of recurrent arch obstruction was 18.2% (6 patients). Four patients (12.1%) had distal obstruction, 1 patient (3%) had proximal obstruction, and 1 patient (3%) had mid-transverse arch obstruction. Five of the 6 patients underwent aortic arch reintervention consisting of four balloon dilatations and two surgical patch aortoplasties. Thirty-one patients advanced to a second-stage procedure, including 30 bidirectional Glenn anastomoses, and 1 Rastelli repair. No significant allosensitization was present in the patients tested.

CONCLUSIONS

The use of bovine pericardium in the Norwood procedure is associated with an acceptable incidence of recurrent arch obstruction. Its availability, lower cost, and possible immunologic advantages make it an attractive alternative to allograft material.

Pediatric Cardiac Transplantation in Children With High Panel Reactive Antibody

BACKGROUND

Elevated panel reactive antibody (PRA) may be considered a risk factor precluding pediatric orthotopic heart transplantation. We retrospectively reviewed our management strategy and outcome data for children undergoing heart transplantation with high PRA (> 10%).

METHODS

Sixty consecutive children (median age = 130.5 days) underwent heart transplantation. Diagnoses included hypoplastic left heart syndrome (HLHS) (30 patients), cardiomyopathy (18 patients), and postoperative complex congenital heart disease (CCHD) (12 patients). Standard induction immunosuppressive therapy included pulse steroids, gamma globulin, and polyclonal rabbit antithymocyte globulin. Initial immunosuppression is a calcinurin inhibitor and an antiproliferative agent. Eight children exhibited elevated PRA (group P). Fifty-two exhibited nonelevated PRA (group N). Immunosuppression was modified in group P as follows: preoperative intravenous immunoglobulin G (IVIG) and/or cyclophosphamide or mycophenolate mofetil and preoperative and postoperative exchange transfusions or plasmapheresis. In group P, cyclophosphamide was the initial antiproliferative agent.

RESULTS

Group P = 4 HLHS patients (all status post [s/p] prior cardiac surgery) and 4 postoperative CCHD patients. Group N = 26 HLHS patients (4 patients s/p prior cardiac surgery), 18 cardiomyopathy patients, and 8 postoperative CCHD patients. Group P patients were older and weighed more than group N patients. Waiting time for donor heart, cardiac ischemic time, and length of hospital stay were similar in both groups. Thirty-day mortality for group P was 25% and for group N it was 7.9% (p = 0.178). Overall mortality for group P was 50% and for group N it was 15.4% (p = 0.043).

CONCLUSIONS

Although heart transplantation can offer children with end-stage heart failure and elevated PRA their only chance of survival, these patients remain high risk despite aggressive immunosuppression.

Cardiac transplantation across a positive prospective lymphocyte cross-match in sensitized recipients

BACKGROUND

Although there is an increasing body of evidence for a deleterious effect of mismatched donor HLA antigens on the outcome of human cardiac transplantation, the role of anti-HLA lymphocytotoxic antibodies remains controversial. Thus, their appearance after cardiac transplantation has been associated with poor outcome by some groups; whereas others have reported them to be of no clinical significance. Furthermore, their presence prior to cardiac transplantation has also been the subject of similarly conflicting reports. The deleterious effect of such pre-existing antibodies has been predicted by a positive lymphocyte cross-match (LCM), which, for most patients awaiting renal transplantation and in many requiring a cardiac allograft, leads to cancellation of the operation. The reason for undertaking the current study was to test the hypothesis that the constraints which a positive LCM result impose in preventing renal transplantation may not apply to orthotopic heart transplantation (OHT).

PATIENTS AND METHODS

Four sensitized patients underwent OHT across a positive prospective LCM. Three were females, and one of those females also underwent cadaveric renal transplantation at the time of OHT. All four patients received aggressive early post-transplant immunosuppressive therapy, which included plasmapheresis, intravenous immunoglobulin (IVIg), antiproliferative agents (cyclophosphamide, basiliximab) and cytokine down-regulators (calcineurin inhibitors, muromonab-CD3) and anticell antibodies (OKT3, ATG). They also received standard immunosuppressive therapy which included corticosteroids. Complement-dependent cytotoxicity (CDC) was used for the identification of anti-HLA lymphocytotoxic antibodies. Reactivity of the latter against more than 10% of a panel of well-characterized T cells was considered sensitization, and required LCM to be performed prospectively, which test was also performed using the CDC technique.

RESULTS

Three of the patients exhibited evidence suggestive of acute or hyperacute rejection in endomyocardial biopsy specimens by postoperative day (POD) 7. Two of the three patients with rejection also exhibited haemodynamic instability (elevated filling pressures and reduced cardiac index) on POD 1, which improved with inotropic support. One patient sustained a cardiac arrest on POD 7, and was successfully resuscitated without sequelae. All patients are now doing well, postoperatively (follow-up: 17-57 months) post-transplant. Two patients have normal left ventricular function and one patient has mild left ventricular dysfunction. Two have no further evidence of sensitization (PRA < 10%).

CONCLUSIONS

Although the number of patients in this study is small, the long-term successful outcome of OHT following positive prospective cross-matches suggests that such a test result, in contrast to the restraints it imposes on renal transplantation, may not be a contra-indication to transplantation of the human heart. If OHT proceeds after the LCM is reported positive, aggressive immunotherapy should not only be initiated early, but should also be targeted at humoral-vascular rejection in particular.

Susceptibility of liver allografts to high or low concentrations of preformed antibodies as measured by flow cytometry

Liver grafts are more resistant to damage by HLA antibodies than other organ allografts, but it is not clear if the antibodies are associated with graft rejection or graft loss, or if different antibody concentrations have different effects. To explore potential associations between antibody concentrations and outcome, preformed IgG antibodies against donor cells were quantified by flow cytometry in 465 consecutive liver transplant recipients. Antibody-positive patients were classified according to whether they had high or low antibody concentrations and analyzed for possible correlation with graft rejection or graft loss. The results showed that the incidence of rejection was not significantly different between antibody-positive and negative patients. However, patients with high antibody concentrations had a higher incidence of steroid-resistant rejections (31% at 1 year) than patients with low antibody (4%) or no antibody (8%, p < 0.0004). These effects were mainly due to T-cell (HLA class 1) antibodies. The overall incidence of rejection at 1 year was 69% for high antibody patients, 51% for patients with low antibodies and 53% for patients with no antibodies (p not significant). In an apparent paradox, antibody-positive patients underwent fewer early graft losses. Thus, the associations of preformed antibodies and outcome depend, on the one hand, on antibody concentrations, and on the other hand on whether the outcome measured is steroid-sensitive rejection, steroid-resistant rejection or graft survival. These complex interactions may explain the controversial results observed in previous studies.

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

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

Plasmapheresis with intravenous immunoglobulin G is effective in patients with elevated panel reactive antibody prior to cardiac transplantation

BACKGROUND

Patients with a PRA >10% are considered to be at greater risk for the development of not only acute cellular and humoral rejection but also increased mortality when compared to nonsensitized patients following transplantation. All patients with a PRA >10% at our institution are treated with plasmapheresis and intravenous immunoglobulin G immediately prior to cardiac transplantation.

METHODS

Sixteen (Group 1) of 118 patients awaiting cardiac transplantation were found to be sensitized. These patients underwent plasmapheresis followed by 20 gm of intravenous immunoglobulin G (IVIG) immediately prior to cardiac transplantation. Group 1 was compared to the remaining 102 patients with a PRA <10% (Group 2).

RESULTS

Despite more patients in Group 1 having a positive crossmatch, pulmonary hypertension, and requiring mechanical circulatory support, there was no statistically significant difference in length of stay or mortality at a mean follow-up of 21.6+/-15.0 months. There was no difference in the occurrence of mild, moderate or severe cellular rejection or humoral rejection in these sensitized patients when compared to Group 2.

CONCLUSIONS

Pretransplant plasmapheresis followed by intravenous immunoglobulin G may be an effective therapy that obviates the need for a prospective crossmatch and allows sensitized patients to undergo cardiac transplantation. There is no increase in the post transplant length of stay, occurrence of rejection or short term mortality. Long term follow up is necessary to evaluate whether there is a difference in the development of late rejection, transplant vasculopathy and survival.

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.

Anti-skeletal muscle glycolipid antibodies in human heart transplantation as predictors of acute rejection: comparison with other risk factors

In forty-five patients who underwent orthotopic heart transplantation, the titer of anti-human skeletal muscle glycolipid antibodies (AGA) present in the sera at the moment of transplantation was correlated with the number of histologically diagnosed cellular grade 3A and humoral acute rejection episodes during the first 120 days after transplantation. Determination of a cutoff value of 0.800 for the AGA level was determined by a receiver operating characteristic curve. Thirteen of 19 patients (68.4%) with an AGA titer above 0.800 developed 24 severe rejection episodes, and of the 26 patients with an AGA titer below 0.800, only 4 (15.3%) presented 6 severe rejection episodes during that time. This was especially evident for the humoral rejection episodes, which were diagnosed in only 1 of the 26 patients with AGA below 0.800 and in 7 of the 19 with AGA above 0.800. Comparison by univariate analysis of other well-known risk factors for a greater number of rejection episodes during the early posttransplant period with the AGA level at the moment of transplantation revealed that the latter distinguished a greater number of patients at risk than the other factors, such as a female donor, the lymphocyte direct cross-match, or the status of the patients at transplantation; the odds ratios were 6.33 for the AGA level, 3.17 for the direct cross-match, and 2.76 for the status at transplantation. By multiple logistic regression analysis, the only relevant risk factors in our group of patients were the AGA level (P=0.0009) and the status at transplantation (P=0.0285). These results indicate that determination of the AGA level at the moment of transplantation could represent a useful method for distinguishing which patients are at risk for a greater number of rejection episodes during the early posttransplant period, with a greater sensitivity than other risk factors.

Detection of alloantibodies by flow cytometry: relevance to clinical transplantation

Before an organ transplant is performed, donor-recipient compatibility must be established by a crossmatch in much the same way as it is done for blood transfusions. The target antigens in organ transplantation, however, are HLA rather than blood group molecules, and the target cells are lymphocytes instead of red cells. If antidonor antibodies are detected, it is important to know whether they are IgG or IgM, whether they recognize T and/or B cells, and whether the antibody reactivity is weak or strong. These test requirements are better met by flow cytometry than by the standard cytotoxicity technique. A growing body of evidence now indicates that flow cytometry can provide more sensitive and timely crossmatch information than cytotoxicity assays to decide whether or not a transplant should be done. Flow cytometry crossmatch (FCXM) is a new and evolving technique that has already been found to be extremely useful in the clinical transplantation setting, even though significant questions yet remain about the precision and reliability of using flow cytometry to quantify alloantibodies and about the limits of normal reactivity in the assay. This article reviews important technical details of the FCXM and its interpretation and clinical application in transplantation medicine.

Pre-transplant anti-epithelial cell antibodies and graft failure after single lung transplantation

Eighty-five patients undergoing single lung transplantation have been studied to determine the presence of anti-epithelial cell antibodies (AECA) prior to transplantation using the human lung carcinoma epithelial cell line A549 in a microcytotoxicity assay. In addition, 29 healthy volunteers were also assayed for the presence of AECA. Twenty-seven of the 85 recipients exhibited AECA prior to transplantation compared to none of the 29 control subjects (p = 0.0001). Actuarial graft survival at 1 year was 78% for the AECA negative group compared to 56% for AECA positive recipients (p = 0.01). No correlation was seen between the presence of AECA and graft rejection as determined by transbronchial biopsy. However, there was an association between AECA and post-transplant infection (p = NS) where 16 (64%) of the AECA positive recipients had postoperative infection episodes compared to 25 (47%) of the negative recipients. Sodium dodecylsulphate polyacrylamide gel electrophoresis and Western blotting was also performed for 68 of the recipients and antibody reactivity was detected in 22 patients compared to 26 patients exhibiting AECA detectable by microcytotoxicity. The presence of AECA demonstrable by Western blotting did not correlate with graft survival, rejection or infection. In conclusion, AECA detectable prior to single lung transplantation are associated with a decrease in graft survival and with postoperative infections.

The effect of panel reactive antibodies and the donor specific crossmatch on graft survival after heart and heart-lung transplantation

Data from 699 cardiac and 290 heart-lung transplants has been analysed to determine the importance of the lymphocytotoxic crossmatch result and panel reactive antibody (PRA) status on graft survival. Donor reactive crossmatching was performed for 636 cardiac transplants. One year actuarial survival for a negative crossmatch (n = 580) was 73% compared to 56% for the positive crossmatch recipients (n = 56) p = 0.0014. Where crossmatches were performed on separated T and B cells, the T cell directed crossmatch was found to be highly predictive of graft failure in 289 cardiac transplants. One year survival for a negative crossmatch was 73% (n = 258), for B cell positive crossmatch recipients 62% (n = 24), and for a positive T cell crossmatch 28% (n = 7) (p = 0.001). Patients' PRA status were grouped into those with negative, medium and high frequencies. There was a trend (not statistically significant) for patients with PRA above 50% to have poor graft survival. Patients with PRA above 50% were significantly more likely to have a positive lymphocytotoxic crossmatch against donor lymphocytes. Donor reactive crossmatching was performed for 283 heart-lung transplants. One year actuarial survival for a negative crossmatch was 61% (n = 251) and for a positive result was 50% (n = 32), p = 0.02.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical orthotopic cardiac transplantation

The results of orthotopic cardiac transplantation have improved dramatically since the early experiences in the late 1960s. After almost 20 years of research and experience and the introduction of cyclosporine, 1 and 5 year survival rates are now 80 percent and 60 percent, respectively. The number of potential recipients far exceeds that of available donors, which is the limiting factor in cardiac transplantation. Complications related to immunosuppressive therapy remain significant, and despite decreased length of hospitalization, costs remain high. The majority of patients have good functional rehabilitation and are free of cardiac symptoms. Moreover, orthotopic cardiac transplantation has finally become a therapeutic treatment of end-stage heart disease.

Purified HLA antigens to probe human alloantibody specificity

HLA class I antigens were purified in sufficient quantities to probe the antigen specificity of lymphocyte and platelet antibodies. Purification of HLA was achieved by affinity chromatography using the monoclonal W6/32 antibody that recognizes a nonpolymorphic determinant of HLA-A,B,C molecules. Pooled platelets from a large number of donors were used as source of antigen. A highly purified HLA preparation was obtained that produced a dose-dependent inhibition of the binding of the W6/32 antibody to lymphocytes as measured by flow cytometry. The binding of monoclonal antibodies to T-lymphocyte antigens or to HLA class II antigens was not affected. The purified HLA also inhibited the binding of lymphocyte alloantibodies from renal transplant patients, providing a direct and definitive way to probe HLA specificity. HLA also inhibited the binding of the same antibodies to platelets but it did not interfere with the binding of alloantibodies to the platelet-specific PLA1 antigen. This preparation, therefore, can conclusively probe the HLA specificity of both alloantibodies for clinical investigation purposes and monoclonal antibodies for screening purposes, and has the potential of becoming a reagent for routine use in clinical and research laboratories.

Organ transplantation and the immune response gene. Clinical correlations and donor requirements

Major gains have been made in the area of clinical organ transplantations due to recent studies concerning the human histocompatibility locus (HLA). These basic science findings, along with developments in clinical pharmacology have allowed for a much broader use of donor sources, and a significant prolongation in clinical life span for these transplantation recipients.