Pediatric Heart Transplantation in Human Leukocyte Antigen–Sensitized Patients

Management of the sensitized pediatric heart transplant patient

Despite advancements in transplant immunosuppression and techniques for managing critically ill patients awaiting heart transplantation, children who are immunologically sensitized to human leukocyte antigen remain at increased risk for morbidity and mortality, both while awaiting and after heart transplant. In this review we will discuss the epidemiology of sensitization, review the immunologic basis and methods of human leukocyte antigen antibody detection, describe outcomes for sensitized pediatric transplant candidates, and consider both pre- and post-transplant management options for sensitized patients.

Molecular events contributing to successful pediatric cardiac transplantation in HLA sensitized recipients

Antibodies to HLA resulting in positive cytotoxicity crossmatch are generally considered a contraindication for cardiac transplantation. However, cardiac transplantations have been performed in children by reducing the Abs and modifying immunosuppression. To identify mechanisms leading to allograft acceptance in the presence of Abs to donor HLA, we analyzed priming events in endothelial cells (EC) by incubating with sera containing low levels of anti-HLA followed by saturating concentration of anti-HLA. Pre-transplant sera were obtained from children with low levels of Abs to HLA who underwent transplantation. EC were selected for donor HLA and exposed to sera for 72 h (priming), followed by saturating concentrations of anti-HLA (challenge). Priming of EC with sera induced the phosphatidylinositol 3-kinase/Akt mediated by the BMP4/WNT pathway and subsequent challenge with panel reactive antibody sera increased survival genes Bcl2 and Heme oxygenase-1, decreased adhesion molecules, induced complement inhibitory proteins and reduced pro-inflammatory cytokines. In contrast, EC which did not express donor HLA showed decreased anti-apoptotic genes. Primed EC, upon challenge with anti-HLA, results in increased survival genes, decreased adhesion molecules, induction of complement inhibitory proteins, and downregulation of pro-inflammatory cytokines which may result in accommodation of pediatric cardiac allografts despite HLA sensitization.

Study rationale, design, and pretransplantation alloantibody status: A first report of Clinical Trials in Organ Transplantation in Children-04 (CTOTC-04) in pediatric heart transplantation

Anti-HLA donor-specific antibodies are associated with worse outcomes after organ transplantation. Among sensitized pediatric heart candidates, requirement for negative donor-specific cytotoxicity crossmatch increases wait times and mortality. However, transplantation with positive crossmatch may increase posttransplantation morbidity and mortality. We address this clinical challenge in a prospective, multicenter, observational cohort study of children listed for heart transplantation (Clinical Trials in Organ Transplantation in Children-04 [CTOTC-04]). Outcomes were compared among sensitized recipients who underwent transplantation with positive crossmatch, nonsensitized recipients, and sensitized recipients without positive crossmatch. Positive crossmatch recipients received antibody removal and augmented immunosuppression, while other recipients received standard immunosuppression with corticosteroid avoidance. This first CTOTC-04 report summarizes study rationale and design and relates pretransplantation sensitization status using solid-phase technology. Risk factors for sensitization were explored. Of 317 screened patients, 290 were enrolled and 240 underwent transplantation. Core laboratory evaluation demonstrated that more than half of patients were anti-HLA sensitized. Greater than 80% of sensitized patients had class I (with or without class II) HLA antibodies, and one-third of sensitized patients had at least 1 HLA antibody with median fluorescence intensity of ≥8000. Logistic regression models demonstrated male sex, weight, congenital heart disease history, prior allograft, and ventricular assist device are independent risk factors for sensitization.

Pediatric heart transplantation across a positive crossmatch: First year results from the CTOTC-04 multi-institutional study

Sensitization is common in pediatric heart transplant candidates and waitlist mortality is high. Transplantation across a positive crossmatch may reduce wait time, but is considered high risk. We prospectively recruited consecutive candidates at eight North American centers. At transplantation, subjects were categorized as nonsensitized or sensitized (presence of ≥1 HLA antibody with MFI ≥1000 using single antigen beads). Sensitized subjects were further classified as complement-dependent cytotoxicity crossmatch (CDC-crossmatch) positive or negative and as donor-specific antibodies (DSA) positive or negative. Immunosuppression was standardized. CDC-crossmatch-positive subjects also received perioperative antibody removal, maintenance corticosteroids, and intravenous immunoglobulin. The primary endpoint was the 1 year incidence rate of a composite of death, retransplantation, or rejection with hemodynamic compromise. 317 subjects were screened, 290 enrolled and 240 transplanted (51 with pretransplant DSA, 11 with positive CDC-crossmatch). The incidence rates of the primary endpoint did not differ statistically between groups; nonsensitized 6.7% (CI: 2.7%, 13.3%), sensitized crossmatch positive 18.2% (CI: 2.3%, 51.8%), sensitized crossmatch negative 10.7% (CI: 5.7%, 18.0%), P = .2354. The primary endpoint also did not differ by DSA status. Freedom from antibody-mediated and cellular rejection was lower in the crossmatch positive group and/or in the presence of DSA. Follow-up will determine if acceptable outcomes can be achieved long-term.

A Review of Induction with Rabbit Antithymocyte Globulin in Pediatric Heart Transplant Recipients

Pediatric heart transplantation (pHTx) represents only a small proportion of cardiac transplants. Due to these low numbers, clinical data relating to induction therapy in this special population are far less extensive than for adults. Induction is used more widely in pHTx than in adults, mainly because of early steroid withdrawal or complete steroid avoidance. Antithymocyte globulin (ATG) is the most frequent choice for induction in pHTx, and rabbit antithymocyte globulin (rATG, Thymoglobulin^®) (Sanofi Genzyme) is the most widely-used ATG preparation. In the absence of large, prospective, blinded trials, we aimed to review the current literature and databases for evidence regarding the use, complications, and dosages of rATG. Analyses from registry databases suggest that, overall, ATG preparations are associated with improved graft survival compared to interleukin-2 receptor antagonists. Advantages for the use of rATG have been shown in low-risk patients given tacrolimus and mycophenolate mofetil in a steroid-free regimen, in sensitized patients with pre-formed alloantibodies and/or a positive donor-specific crossmatch, and in ABO-incompatible pHTx. Registry and clinical data have indicated no increased risk of infection or post-transplant lymphoproliferative disorder in children given rATG after pHTx. A total rATG dose in the range 3.5–7.5 mg/kg is advisable.

The clinical impact of donor-specific antibodies in heart transplantation

Donor-specific antibodies (DSA) are integral to the development of antibody-mediated rejection (AMR). Chronic AMR is associated with high mortality and an increased risk for cardiac allograft vasculopathy (CAV). Anti-donor HLA antibodies are present in 3-11% of patients at the time of heart transplantation (HTx), with de novo DSA (predominantly anti-HLA class II) developing post-transplant in 10-30% of patients. DSA are associated with lower graft and patient survival after HTx, with one study suggesting a three-fold increase in mortality in patients who develop de novo DSA (dnDSA). DSA against anti-HLA class II, notably DQ, are at particularly high risk for graft loss. Although detection of DSA is not a criterion for pathologic diagnosis of AMR, circulating DSA are found in almost all cases of AMR. MFI thresholds of ~5000 for DSA against class I antibodies, 2000 against class II antibodies, or an overall cut-off of 5-6000 for any DSA, have been suggested as being predictive for AMR. There is no firm consensus on pre-transplant strategies to treat HLA antibodies, or for the elimination of antibodies after diagnosis of AMR. Minimizing the risk of dnDSA is rational but data on risk factors in HTx are limited. The effect of different immunosuppressive regimens is largely unexplored in HTx, but studies in kidney transplantation emphasize the importance of adherence and maintaining adequate immunosuppression. One study has suggested a reduced risk for dnDSA with rabbit antithymocyte globulin induction. Management of DSA pre- and post-HTx varies but typically most centers rely on a plasmapheresis or immunoadsorption, with or without rituximab and/or intravenous immunoglobulin. Based on the literature and a multi-center survey, an algorithm for a suggested surveillance and therapeutic strategy is provided.

Charges and resource utilization for pediatric heart transplantation across a positive virtual and/or cytotoxicity crossmatch

There is growing acceptance of transplantation across a positive crossmatch for highly allosensitized pediatric HT candidates. While survival may be similar to patients transplanted across a negative crossmatch, costs are unknown. Among 60 HT recipients at our center from 5/07 to 6/12, we analyzed hospital charges and length of stay from the day of HT to discharge and through the first year after transplant. Median age at HT was 6.2 years (15 days-20.5 years). Charges in the first year post-HT were greater for crossmatch-positive patients ($907 678 vs $549 754; P = .017), with a trend toward higher charges for the HT hospitalization ($537 640 vs $407 374; P = .07). Plasmapheresis was more common in crossmatch-positive patients during the HT hospitalization (80% vs 4%, P < .001). In the first year after HT, crossmatch-positive patients had a greater number of endomyocardial biopsies (10 vs 7.5, P = .03) and episodes of treated rejection (2 vs 0, P = .004). Pediatric HT across a positive crossmatch is associated with higher first-year costs, including increased use of plasmapheresis and care around an increased number of rejections. These novel data will help inform decision and policymaking regarding care practices for the growing population of highly sensitized pediatric HT candidates.

Long-term outcomes of simultaneous heart and kidney transplantation in pediatric recipients

Pediatric sHKTx has become an effective therapy for patients with combined cardiac and renal failure. Often, these patients develop human leukocyte antigen antibodies from their previous allografts and are therefore more difficult to re-transplant. We describe the largest case series of a predominantly sensitized pediatric sHKTx with emphasis on medical management and patient outcomes. Demographics, clinical characteristics, antibody, and biopsy data were retrospectively collected from University of California, Los Angeles database and correlated with short- and long-term patient and allograft outcomes of all sHKTx performed between 2002 and 2015. We identified seven pediatric patients who underwent sHKTx at our center. Mean age at time of sHKTx was 13.7 years and 85.7% were re-graft patients. 57.1% were sensitized with cPRA >50% and another 57.1% had preformed donor-specific antibody. Five-year renal allograft survival and patient survival was 85.7% for both end-points. The remaining six patients are all alive (mean follow-up 78.5 months) with good kidney and heart function. sHKTx in a population with increased immunological risk can be associated with good long-term outcomes and offers potential guidance to the pediatric transplant community where data are limited.

Heart Transplantation-The Pediatric Cardiac Critical Care Perspective

OBJECTIVES

Although there have been tremendous advancements in the care of severe pediatric cardiovascular disease, heart transplantation remains the standard therapy for end-stage heart disease in children. As such, these patients comprise an important and often complex subset of patients in the ICU. The purpose of this article is to review the causes and management of allograft dysfunction and the medications used in the transplant population.

DATA SOURCES

MEDLINE, PubMed, and Cochrane Database of systemic reviews.

CONCLUSIONS

Pediatric heart transplant recipients represent a complex group of patients that frequently require critical care. Their immunosuppressive medications, while being vital to maintenance of allograft function, are associated with significant short- and long-term complications. Graft dysfunction can occur from a variety of etiologies at different times following transplantation and remains a major limitation to long-term posttransplant survival.

Pediatric Cardiac Intensive Care Society 2014 Consensus Statement: Pharmacotherapies in Cardiac Critical Care Immune Therapy

OBJECTIVE

In this Consensus Statement, we review the etiology and pathophysiology of inflammatory processes seen in critically ill children with cardiac disease. Immunomodulatory therapies aimed at improving outcomes in patients with myocarditis, heart failure, and transplantation are extensively reviewed.

DATA SOURCES

The author team experience and along with an extensive review of the medical literature were used as data sources.

DATA SYNTHESIS

The authors synthesized the data in the literature to present current immumodulatory therapies. For each drug, the physiologic rationale, mechanism of action, and pharmacokinetics are synthesized, and the evidence in the literature to support the therapy is discussed.

CONCLUSIONS

Immunomodulation has a crucial role in the treatment of certain pediatric cardiac diseases. Immunomodulatory treatments that have been used to treat myocarditis include corticosteroids, IV immunoglobulin, cyclosporine, and azathioprine. Contemporary outcomes of pediatric transplant recipients have improved over the past few decades, partly related to improvements in immunomodulatory therapy to prevent rejection of the donor heart. Immunosuppression therapy is commonly divided into induction, maintenance, and acute rejection therapy. Common induction medications include antithymocyte globulin, muromonab-CD3, and basiliximab. Maintenance therapy includes chronic medications that are used daily to prevent rejection episodes. Examples of maintenance medications are corticosteroids, cyclosporine, tacrolimus, sirolimus, everolimus, azathioprine, and mycophenolate mofetil. Rejection of the donor heart is diagnosed either by clinically or by biopsy and is treated with intensification of immunosuppression.

Current challenges in pediatric heart transplantation for congenital heart disease

PURPOSE OF REVIEW

Pediatric heart transplantation is an established therapy for end-stage cardiac disease without suitable medical or surgical options. However, transplantation for congenital heart disease carries an incremental risk that challenges the pediatric transplant team on multiple levels.

RECENT FINDINGS

With improved outcomes following palliative and corrective congenital cardiac surgery, cardiac transplantation has decreased in recent years as a primary therapy. Nevertheless, congenital heart disease remains the most common indication for cardiac transplantation during infancy. Primary transplantation in infancy is selectively recommended for severe systemic ventricular dysfunction, severe atrioventricular valve insufficiency, and occlusive coronary artery anomalies, particularly with single ventricle physiology. Wait-list mortality remains highest for infants with prior palliative surgery and patients with failing Fontan physiology, both of whom have limited options for effective mechanical circulatory support. The sensitized patient carries an increased risk with prolonged wait times, although virtual cross-matches and single bead assays for donor-specific antigens have facilitated the transplant process. Early and late survival after transplantation for congenital heart disease remain inferior to cardiomyopathy, with prior Fontan procedure as a major risk factor. However, among survivors at 6 months, late outcomes are generally excellent. Major late causes of death include allograft vasculopathy, post-transplant lymphoproliferative disease, and acute rejection. Noncompliance with medications remains a major risk for teenage mortality.

SUMMARY

Despite the myriad of evolving challenges, pediatric heart transplantation for congenital heart disease enjoys routine short and long-term success at experienced centers for the vast majority of such patients without other options.

Comparison of listing strategies for allosensitized heart transplant candidates requiring transplant at high urgency: a decision model analysis

Allosensitized children who require a negative prospective crossmatch have a high risk of death awaiting heart transplantation. Accepting the first suitable organ offer, regardless of the possibility of a positive crossmatch, would improve waitlist outcomes but it is unclear whether it would result in improved survival at all times after listing, including posttransplant. We created a Markov decision model to compare survival after listing with a requirement for a negative prospective donor cell crossmatch (WAIT) versus acceptance of the first suitable offer (TAKE). Model parameters were derived from registry data on status 1A (highest urgency) pediatric heart transplant listings. We assumed no possibility of a positive crossmatch in the WAIT strategy and a base-case probability of a positive crossmatch in the TAKE strategy of 47%, as estimated from cohort data. Under base-case assumptions, TAKE showed an incremental survival benefit of 1.4 years over WAIT. In multiple sensitivity analyses, including variation of the probability of a positive crossmatch from 10% to 100%, TAKE was consistently favored. While model input data were less well suited to comparing survival when awaiting transplantation across a negative virtual crossmatch, our analysis suggests that taking the first suitable organ offer under these circumstances is also favored.

Challenges with sensitized recipients in pediatric heart transplantation

The sensitization of patients to human leukocyte antigens prior to heart transplantation is increasingly being recognized as an important challenge both before and after the transplant, and the effects of sensitization on clinical outcomes are just beginning to be understood. Many patients are listed with the requirement of a negative prospective or virtual crossmatch prior to accepting a donor organ. This strategy has been associated with both longer waitlist times and higher waitlist mortality. An alternative approach is to transplant across a potentially positive crossmatch while utilizing strategies to decrease the significance of the human leukocyte antigen antibodies. This review will examine the challenges and the impact of sensitization on pediatric patients prior to and following heart transplantation.

Heart transplant after the Fontan operation

Although the Fontan operation may provide a durable circulation for some patients with functionally univentricular hearts for several decades, circulatory failure becomes more common over time. Medical and/or surgical interventions can improve the circulation for some period of time; however, many patients will experience end-stage circulatory failure. Heart transplantation may be considered in these patients. This review will cover the indications and evaluation for heart transplantation, management of patients while waiting for heart transplantation and the current outcomes of transplantation in this population.

Antibody depletion for the treatment of crossmatch-positive pediatric heart transplant recipients

Sensitization to HLA is a risk factor for adverse outcomes after heart transplantation. Requiring a negative prospective CM results in longer waiting times and increased waitlist mortality. We report outcomes in a cohort of sensitized children who underwent transplant despite a positive CDC CM+ using a protocol of antibody depletion at time of transplant, followed by serial IVIG administration. All patients <21 yrs old who underwent heart transplantation at Boston Children's Hospital from 1/1998 to 1/2011 were included. We compared freedom from allograft loss, allograft rejection, and serious infection between CM+ and CM- recipients. Of 134 patients in the cohort, 33 (25%) were sensitized prior to transplantation and 12 (9%) received a CM+ heart transplant. Serious infection in the first post-transplant year was more prevalent in the CM+ patients compared with CM- patients (50% vs. 16%; p = 0.005), as was HD-AMR (50% vs. 2%; p < 0.001). There was no difference in freedom from allograft loss or any rejection. At our center, children transplanted despite a positive CM had acceptable allograft survival and risk of any rejection, but a higher risk of HD-AMR and serious infection.

Quantification, identification, and relevance of anti-human leukocyte antigen antibodies formed in association with the berlin heart ventricular assist device in children

BACKGROUND

Ventricular assist devices (VADs) are increasingly being used in pediatric patients to provide long-term cardiac support. One potential complication of VAD therapy is the development of antibodies directed against human leukocyte antigens (HLA). This phenomenon has not been well described with the Berlin Heart EXCOR VAD, the most commonly used VAD in pediatric patients.

METHODS

The records of all pediatric patients undergoing VAD support using the Berlin Heart device at our institution between April 2005 and August 2011 were reviewed retrospectively. Demographic and clinical data regarding the VAD course were collected. Assessment of anti-HLA antibodies was performed using Luminex, and antibodies were quantified using mean fluorescence intensity (MFI). Assessment for anti-HLA antibodies was performed before VAD implantation and in serial fashion after VAD implantation. Clinically significant anti-HLA antibodies (sensitization) were defined by an MFI of more than 1000.

RESULTS

Thirty-six patients were supported with the Berlin Heart VAD; 13 met inclusion criteria. The majority (85%) carried the diagnosis of dilated cardiomyopathy. Evidence of sensitization pre-VAD was found in 69%; new-onset sensitization (the development of new antibodies on VAD) occurred in 69%. All patients survived to transplantation. In two patients, the retrospective crossmatch was positive, but only in one patient was the crossmatch positive for antibodies formed while on VAD.

CONCLUSIONS

Using Luminex and MFI quantification, anti-HLA antibodies are common before VAD implantation in pediatric patients. While on VAD support, new anti-HLA antibodies formed in a majority, but the immediate impact of these antibodies appears to be limited.

Donor-specific antibodies: can they predict C4d deposition in pediatric heart recipients?

There is limited evidence regarding the utility of circulating DSA in surveillance for AMR of pediatric heart recipients. Our hypothesis is that quantitation of DSA improves their power for predicting a C4d+, an integral component in the current diagnostic criteria of AMR. All pediatric recipients transplanted between 10/2005 and 1/2011 were retrospectively reviewed for DSA determined within 48 h of EMB. C4d+ was defined as >25% endothelial cell staining by immunohistochemical methods. A total of 183 paired DSA-EMB determinations were identified in 60 patients, a median of three paired studies per patient (range: 1-9). DSA were detected in 60 of these determinations. A receiver-operating characteristic plot identified a threshold single-antibody MFI of >6000 that strongly correlated with C4d+ (p < 0.0001) with a high negative predictive value (0.97) and specificity (0.95). The sensitivity and positive predictive values were 0.71 and 0.60, respectively. The predictive power of single-antigen DSA for C4d deposition was improved in pediatric heart recipients using an institution-specific MFI threshold value. In post-transplant care, quantitative DSA should be an essential component in the surveillance for AMR.

Heart Transplant with Donor-Specific Antibody after Immunoadsorption plus Rituximab: A Case Report

Different desensitization strategies are available for treating patients with preformed human leukocyte antigen (HLA) antibodies. A highly presensitized heart recipient received immunoadsorption and rituximab therapy. The patient, with end-stage heart failure, was positive only for antibodies of HLA class I (anti-A2, A10, B17), and Luminex platform (One Lambda kit) showed a panel-reactive antibody score of 64%. The patient's serum was tested repeatedly in both complement-dependent cytotoxicity and flow-cytometry crossmatches against cells from different potential organ donors. The results of these crossmatches were positive on flow cytometry when tested with HLA-A2, A10, and B17 but were still negative on cytotoxicity. The patient was treated with a desensitization regimen; this treatment immediately decreased antibody levels of 70% and the patient subsequently received a transplant with donor-specific HLA antibody (HLA-A2). After more than 2 years, graft function remains normal and the clinical status of the patient is stable.

Postoperative care of the transplanted patient

The successful delivery of optimal peri-operative care to pediatric heart transplant recipients is a vital determinant of their overall outcomes. The practitioner caring for these patients must be familiar with and treat multiple simultaneous issues in a patient who may have been critically ill preoperatively. In addition to the complexities involved in treating any child following cardiac surgery, caretakers of newly transplanted patients encounter multiple transplant-specific issues. This chapter details peri-operative management strategies, frequently encountered early morbidities, initiation of immunosuppression including induction, and short-term outcomes.

Immunologic considerations in heart transplantation for congenital heart disease

Children and adults with congenital heart disease (CHD) can require interventions that result in immunologic alterations that are different than those seen in patients with cardiomyopathies. Patients with CHD can be exposed to heart surgeries, blood products, valved and non-valved allograft tissue, and mechanical circulatory support, all of which can alter the immunologic status of these patients. This change in immunologic status is most commonly manifested as the development of anti-human leukocyte antigen (HLA) antibodies. This review will delineate a) the causes of anti-HLA anti-body production (often referred to as allosensitization); b) preventive strategies for anti-HLA antibody production before transplantation; c) treatment strategies for those patients who develop anti-HLA antibodies before transplantation; d) consequences of HLA allosensitization after transplantation; and e) treatment of HLA allosensitization and antibody-mediated rejection after transplantation.

Outcomes after listing with a requirement for a prospective crossmatch in pediatric heart transplantation

BACKGROUND

Allosensitization is associated with inferior waitlist outcomes in pediatric heart transplant candidates, presumably because of the requirement for a negative prospective crossmatch. However, there are no reports of heart transplant candidate outcomes according to prospective crossmatch requirements.

METHODS

We analyzed data on all children listed for isolated heart transplantation from 1995 to 2009 in the USA according to prospective crossmatch requirement (PXMR). Primary objectives were to describe the prevalence of PXMR at and during listing and to compare waitlist and post-transplant survival for patients based on PXMR. Patients with a PXMR during listing include those with a PXMR at the time of listing as well as those who were designated by the listing center as needing a prospective crossmatch at some point after being placed onto the waitlist.

RESULTS

Among 6,343 listed children, 7.7% had a requirement for a prospective crossmatch at the time of listing and 11.8% had a requirement for a prospective crossmatch during listing. After controlling for risk factors associated with inferior survival, PXMR at listing was associated with increased waitlist mortality (HR 1.32, 95% CI 1.10 to 1.56; p = 0.003). Recipients with a PXMR during listing more commonly had a positive DSXM (22.1% vs 10.3%, p < 0.0001), as did recipients who carried a PXMR throughout listing (21.7% vs 11.3%, p = 0.004). However, there was no significant difference in post-transplant survival on the basis of a PXMR during listing (HR 1.04, 95% CI 0.87 to 1.25; p = 0.67). Nearly 30% of recipients with a PXMR during listing had a peak pre-transplant PRA ≤ 10%.

CONCLUSIONS

PXMR increases the likelihood of death while awaiting, but not after, pediatric heart transplantation. Further study is necessary to understand how PXMR is applied, and changes, after listing for pediatric heart transplantation.

Cardiac antibody-mediated rejection

Many factors limit short- and long-term survival after pediatric heart transplantation. Historically, attention had been directed toward T-cell responses and acute cellular rejection. Presence of pretransplant antibodies against HLA is associated with increased donor wait times and poor post-transplant outcomes. Therapies aimed to mitigate circulating antibodies include plasmapheresis, protein A immunoadsorption columns, intravenous immune globulin, rituximab, and bortezomib. The negative effects of B cells, HLA antibodies, and AMR and potential interventions are the focus of this review article.

Heart transplantation in adults with end-stage congenital heart disease

Residual abnormalities in cardiac structure and function predispose adults with congenital heart disease to late-onset heart failure and its complications. Evaluation of this population requires collaboration between adult congenital and heart failure specialists. In addition to assessing heart transplant eligibility, clinicians must balance the risks of premature listing against progressive heart failure and increased waiting list mortality. Following heart transplantation, adults with congenital heart disease have higher mortality due to an increased risk of bleeding, infection and donor right heart failure secondary to pulmonary hypertension. Concerns relating to increased early mortality should be balanced against superior long-term survival in adult congenital heart disease patients surviving beyond the first year after heart transplantation.

Outcomes in pediatric cardiac transplantation with a positive HLA cross-match

Previous studies have shown poor outcomes in pediatric heart transplant recipients with a high PRA or a positive direct donor-recipient cross-match. This study describes outcomes in patients with a positive cross-match at a large pediatric program. Pediatric heart transplant patients at a large single center between January 1993 and July 2009 were reviewed; those with cross-match data were analyzed. Cross-match data were available in 242/262 (92.4%) patients. Indications for transplant were cardiomyopathy (58%), CHD (32%), and retransplant (7%). PRA was ≥10% in 31/213 (14.6%) patients. A retrospective cross-match was positive in 17/31 (55%) patients with PRA ≥10% and 0/182 with PRA <10%. In positive cross-match patients, rejection frequency in the first year post-transplant was higher than negative cross-match patients (1.69 vs. 0.96 episodes/pt year, p = 0.014). There was no difference in rejection frequency after the first year post-transplant (0.18 vs. 0.12 episodes/pt year, p = 0.14). Overall survival was not significantly different between the groups with a median follow-up time of 4.5 yr. Heart transplantation in patients with a positive cross-match may result in good medium-term survival but a higher frequency of early rejection. Further investigation is warranted to define which patients with a positive cross-match will do poorly.

Management of children undergoing cardiac transplantation with high Panel Reactive Antibodies

Highly sensitised children in need of cardiac transplantation have overall poor outcomes because of increased risk for dysfunction of the cardiac allograft, acute cellular and antibody-mediated rejection, and vasculopathy of the cardiac allograft. Cardiopulmonary bypass and the frequent use of blood products in the operating room and cardiac intensive care unit, as well as the frequent use of homografts, have predisposed potential recipients of transplants to allosensitisation. The expansion in the use of ventricular assist devices and extracorporeal membrane oxygenation has also contributed to increasing rates of allosensitisation in candidates for cardiac transplantation. Antibodies to Human Leukocyte Antigen can be detected before transplantation using several different techniques, the most common being the "complement-dependent lymphocytotoxicity assays". "Solid-phase assays", particularly the "Luminex® single antigen bead method", offer improved specificity and more detailed information regarding specificities of antibodies, leading to improved matching of donors with recipients. Allosensitisation prolongs the time on the waiting list for potential recipients of transplantation and increases the risk of complications and death after transplantation. Aggressive reduction of antibodies to Human Leukocyte Antigen in these high-risk patients is therefore of vital importance for long-term survival of the patient and cardiac allograft. Strategies to decrease Panel Reactive Antibody or percent reactive antibody before transplantation include plasmapheresis, intravenous administration of immunoglobulin, and specific treatment to reduce B-cells, particularly Rituximab. These strategies have resulted in varying degrees of success. Antibody-mediated rejection and cardiac allograft vasculopathy are two of the most important complications of transplantation in patients with high Panel Reactive Antibody. The treatment of antibody-mediated rejection in recipients of cardiac transplants is largely empirical and includes the use of high-dose corticosteroids, plasmapheresis, intravenous administration of immunoglobulins, anti-thymocyte globulin, and Rituximab. Cardiac allograft vasculopathy is believed to be secondary to chronic complement-mediated endothelial injury and chronic vascular rejection. The use of proliferation signal inhibitors, such as sirolimus and everolimus, has been shown to delay the progression of cardiac allograft vasculopathy. In some non-sensitised recipients of cardiac transplants, the de novo formation of antibodies to Human Leukocyte Antigen after transplantation may increase the likelihood of adverse clinical outcomes. The use of serial testing for donor-specific antibodies after cardiac transplantation may be advisable in patients with frequent episodes of rejection and patients with history of sensitisation. Allosensitisation before transplantation can negatively influence outcomes after transplantation. A high incidence of antibody-mediated rejection and graft vasculopathy can result in graft failure and decreased survival. Current strategies to decrease allosensitisation have helped to expand the pool of donors, improve times on the waiting list, and decrease mortality. Centres of transplantation offering desensitisation are currently using plasmapheresis to remove circulating antibodies; intravenous immunoglobulin to inactivate antibodies; cyclophosphamide to suppress B-cell proliferation; and Rituximab to deplete B-lymphocytes. Similar approaches are also used to treat antibody-mediated rejection after transplantation with promising results.

Allosensitization and outcomes in pediatric heart transplantation

BACKGROUND

Allosensitization among children being considered for heart transplantation remains a great challenge. Controversy exists as to the best approach for those with elevated panel-reactive antibody (PRA) titers. We sought to define the association between elevated PRA and outcomes using data from the multi-institutional Pediatric Heart Transplant Study Group.

METHODS

Between January 1993 and December 2008, 3,016 patients (>1 month of age) were listed for heart transplantation. PRA data at listing were available for 2,500 (83%) patients, and 2,237 underwent transplantation with PRA data being available for 1,904 (85%). Because various PRA assays were employed (e.g., cell-based and solid phase) we entered the highest value regardless of methodology.

RESULTS

Among the factors associated with high PRA at transplant were Status 1 at listing, previous sternotomy and prior Norwood procedure. An elevated PRA at listing was associated with higher risk of death while waiting. Of subjects with PRA ≥ 50% only 57% were transplanted by 1 year on the waitlist, as compared with 76% of those with PRA <10%. Waitlist mortality for the highly allosensitized subjects (≥ PRA 50%) was 19% by 12 months. Survival at 1 year after transplantation was significantly lower in those with PRA ≥ 50% versus those with PRA <10% (73% vs 90%, respectively, p < 0.0001). Those with elevated PRA who had a negative prospective crossmatch had no difference in survival compared with those without allosensitization. There was no significant association between PRA levels and time to first rejection or development of coronary allograft vasculopathy.

CONCLUSIONS

Significant allosensitization is associated with more than a 2-fold increased risk of death within the first transplant year. Although prospective crossmatching abrogates the risk of post-transplant mortality, it may contribute to higher pre-transplant attrition due to longer waitlist times. There is a critical need for strategies to minimize the impact of allosensitization and antibody-mediated rejection immediately after transplantation.

Immunosuppression therapy for pediatric heart transplantation

OPINION STATEMENT

Outcomes following cardiac transplantation in childhood continue to improve. Advances in immunosuppressive therapy over the past two decades likely have contributed to this trend. The evolution in the management of immunosuppression in children has been based on clinical experience rather than on evidence-based medicine; indeed, there have been no pivotal randomized controlled trials of any form of immunosuppression in pediatric thoracic transplantation. Important trends in immunosuppressive therapy and transplant outcomes have been obtained from large transplant registries. Several trends have been identified since the last review of this topic in this journal. First, there is increased knowledge of the pharmacodynamics and pharmacokinetics of immunosuppressive drugs in children, with notable advances in the field of pharmacogenomics. These studies help explain individual variations in drug exposure, efficacy, and adverse events. They also help explain racial and ethnic variations in drug metabolism and efficacy. Second, there have been clear trends in the use of specific immunosuppressive medications. Use of induction therapy, especially polyclonal T cell-depleting antibody preparations, has increased significantly in recent years. The calcineurin inhibitor (CNI) tacrolimus is being used as the cornerstone of maintenance therapy in lieu of cyclosporine in more and more centers. Mounting evidence suggests that use of adjunctive agents (notably mycophenolate mofetil [MMF]) may improve outcomes, including survival, suggesting that monotherapy with CNIs is not the ideal maintenance therapy. Despite its increased cost, MMF has largely replaced azathioprine as the adjunctive agent of choice. Inhibitors of the mammalian target of rapamycin (i.e., sirolimus and everolimus) have not yet assumed a major place as adjunctive agents, as their safety and efficacy have not been well established in children. With the improvements in immunosuppressive therapy, the justification for routine corticosteroid use is far from clear, and many centers have shown excellent outcomes with complete steroid avoidance. Third, there is increasing interest in the importance of anti-HLA antibodies as important risk factors for adverse graft and patient outcomes. This is generating intense interest in treatments that target B cells and plasma cells. Finally, there is increasing realization that the "one size fits all" approach to immunosuppressive therapy is an obsolete concept and that the ultimate goal is to tailor immunosuppressive therapy to the needs of the individual patient. The development of reliable biomarkers of the patient's immune response to the allograft will be essential for optimal individualized immunosuppressive management.

Report from a consensus conference on antibody-mediated rejection in heart transplantation

BACKGROUND

The problem of AMR remains unsolved because standardized schemes for diagnosis and treatment remains contentious. Therefore, a consensus conference was organized to discuss the current status of antibody-mediated rejection (AMR) in heart transplantation.

METHODS

The conference included 83 participants (transplant cardiologists, surgeons, immunologists and pathologists) representing 67 heart transplant centers from North America, Europe, and Asia who all participated in smaller break-out sessions to discuss the various topics of AMR and attempt to achieve consensus.

RESULTS

A tentative pathology diagnosis of AMR was established, however, the pathologist felt that further discussion was needed prior to a formal recommendation for AMR diagnosis. One of the most important outcomes of this conference was that a clinical definition for AMR (cardiac dysfunction and/or circulating donor-specific antibody) was no longer believed to be required due to recent publications demonstrating that asymptomatic (no cardiac dysfunction) biopsy-proven AMR is associated with subsequent greater mortality and greater development of cardiac allograft vasculopathy. It was also noted that donor-specific antibody is not always detected during AMR episodes as the antibody may be adhered to the donor heart. Finally, recommendations were made for the timing for specific staining of endomyocardial biopsy specimens and the frequency by which circulating antibodies should be assessed. Recommendations for management and future clinical trials were also provided.

CONCLUSIONS

The AMR Consensus Conference brought together clinicians, pathologists and immunologists to further the understanding of AMR. Progress was made toward a pathology AMR grading scale and consensus was accomplished regarding several clinical issues.

Outcomes of cardiac transplantation in highly sensitized pediatric patients

Despite aggressive immunosuppressive therapy, pediatric orthotopic heart transplant (OHT) candidates with elevated pre-transplant panel reactive antibody (PRA) carry an increased risk of rejection and early graft failure following transplantation. This study has aimed to more specifically evaluate the outcomes of transplant candidates stratified by PRA values. Records of pediatric patients listed for OHT between April 2004 and July 2008 were reviewed (n = 101). Survival analysis was performed comparing patients with PRA < 25 to those with PRA > 25, as well as patients with PRA < 80 and PRA > 80. Patients with PRA > 25 had decreased survival compared with those with PRA < 25 after listing (P = 0.004). There was an even greater difference in survival between patients with PRA > 80 and those with PRA < 80 (P = 0.002). Similar analyses for the patients who underwent successful transplantation showed no significant difference in post-transplant survival between patients with a pre-transplant PRA > 25 and those with PRA < 25 (P = 0.23). A difference approaching significance was noted for patients with PRA > 80 compared with PRA < 80 (P = 0.066). Patients with significantly elevated pre-transplant PRAs at the time of listing have a significantly worse outcome compared to those with moderately increased PRA values or non-sensitized patients. Further study is necessary to guide physician and family treatment decisions at the time of listing.

Heart transplantation for heart failure in children

Heart transplantation has become standard therapy for end-stage heart failure in children with cardiomyopathy as well as complex congenital heart disease, and has a significant effect on survival and quality of life. The indications for listing and referral for transplantation are outlined. Evaluation for heart transplantation is discussed, including full pretransplant assessment. ABO incompatible listing and HLA sensitization are discussed, and listing algorithms are outlined for different countries.

Impact of ABO-incompatible listing on wait-list outcomes among infants listed for heart transplantation in the United States: a propensity analysis

BACKGROUND

The purported advantage of ABO-incompatible (ABO-I) listing is to reduce wait times and wait-list mortality among infants awaiting heart transplantation. We sought to describe recent trends in ABO-I listing for US infants and to determine the impact of ABO-I listing on wait times and wait-list mortality.

METHODS AND RESULTS

In this multicenter retrospective cohort study using Organ Procurement and Transplant Network data, infants<12 months of age listed for heart transplantation between 1999 and 2008 (n=1331) were analyzed. Infants listed for an ABO-I transplant were compared with a propensity score-matched cohort listed for an ABO-compatible transplant through the use of a Cox shared-frailty model. The primary end point was time to heart transplantation. The percentage of eligible infants listed for an ABO-I heart increased from 0% before 2002 to 53% in 2007 (P<0.001 for trend). Compared with infants listed exclusively for an ABO-compatible heart, infants with a primary ABO-I listing strategy (n=235) were more likely to be listed 1A, to have congenital heart disease and renal failure, and to require extracorporeal membrane oxygenation. For the propensity score-matched groups (n=197 matched pairs), there was no difference in wait-list mortality; however, infants with blood type O assigned an ABO-I listing strategy were more likely to undergo heart transplantation by 30 days (31% versus 16%; P=0.007) with a less pronounced effect for infants with other blood types.

CONCLUSIONS

The proportion of US infants listed for an ABO-I heart transplantation has risen dramatically in recent years but still appears to be preferentially used for sicker infant candidates. The ABO-I listing strategy is associated with a higher likelihood of transplantation within 30 days for infants with blood group O and may benefit a broader range of transplantation candidates.

Heart transplantation in children

In the last 40 years, orthotopic heart transplantation has been established as a realistic treatment strategy for infants and children with severe forms of congenital heart disease and cardiomyopathy. The evaluation, management, and outcomes of these patients have continued to improve. These achievements have advanced pediatric cardiac transplantation and allowed more attention to be focused on improving quality of life after transplantation and reducing the long-term complications.

Lessons from cardiac transplantation in infancy

Besides correcting devastating pathophysiology, cardiac transplantation in infancy offers an incomparable model for exploring the structure and function of the immune system. Infants and young children have relatively few memory B cells and T cells. Hence, the response of the young to allotransplantation better represents a primary immune response and may be better suited to testing spontaneous tolerance. Those who undergo cardiac transplantation in infancy are also unique because they are often subjected to thymectomy and depletion of mature T cells. These subjects can have a dramatic contraction of T cell diversity, allowing the testing of how diversity contributes to function.

Continuous infusion of thymoglobulin for induction therapy in pediatric heart transplant recipients; experience and outcomes with a novel strategy for administration

Minimal data exist on the perioperative use of TG for induction in pediatric HTx recipients. We report our experience using continuous infusion of TG on (i) perioperative adverse events, (ii) rejection, (iii) CAV, and (iv) PTLD. TG was infused via peripheral intravenous intra- and perioperatively as a continuous infusion (24 h/day). Starting dose was 1.5 mg/kg/day titrated to achieve target lymphocyte count of 0.1-0.3 x 10(9)/L. Fifty-five patients received TG; mean age at HTx was 4.4 yr (1 day-17.8 yr). The mean duration of TG was three and a half days (2-7 days). Median platelet count during TG infusion was 95 x 10(9)/L (28-228). Five patients had TG stopped for low platelets (at 4-6 days post-HTx) - all started maintenance immunosuppression. There was no perioperative mortality due to infection. Mean follow-up of 46 survivors was 2.3 yr (0.6-5.8 yr). Fifty-one percent had > or = ISHLT 2R rejection at a median time of 33 days post-HTx (7 days-2 yr). One patient developed PTLD 1.4 yr post-HTx; three patients developed mild-moderate CAV. TG as a continuous infusion appears to have a good safety profile. Though mild thrombocytopenia was prevalent, there was no bleeding attributable solely to TG. Whether early depletion of T-cell function will translate into long-term benefits remains to be determined.