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

Single center experience with ABO-incompatible and ABO-compatible pediatric heart transplantation

Introduction

The aim of this study was to analyze the results after pediatric heart transplantation (pHTx) at our single center differentiating between ABO-incompatible (ABOi) and -compatible (ABOc) procedures.

Methods and patients

We retrospectively analyzed outcomes of ABO-incompatible HTx procedures performed at our center and compared the data to ABO-compatible HTx of the same era. Eighteen children (<17 months) underwent pediatric HTx and seven of them underwent ABO-incompatible HTx between 2003 and 2015.

Results

Mechanical circulatory support as bridge to transplant was necessary in 3/7 patients before ABO-incompatible HTx and in 3/11 patients before ABO-compatible HTx. Mean waiting time on the list was 36 ± 30 days for ABO-incompatible HTx and 86 ± 65 days for ABO-compatible HTx. The 5-years re-transplant free survival was 86% following ABO-incompatible and 91% after ABO-compatible. In the cohort undergoing ABO-incompatible HTx, 2 patients showed an acute cellular rejection, while early graft failure was not observed. In the cohort undergoing ABOcompatible HTx, acute cellular rejection was observed in 9/11 patients, with early graft failure occurring in nine and CVP in two. A total of ten children were listed for ABO-incompatible HTx after 2015; however, all ten underwent an ABO-compatible transplantation.

Discussion

This study adds much needed information to the literature on ABOi-HTx by showing with a retrospective single center analysis that it is safe and leads to shorter waiting times. We conclude that strategies for ABOi-HTx should be elaborated further, potentially allowing more timely transplantation and thereby preventing waiting list complications such as the need for mechanical circulatory support and even death.

ABO-incompatible heart transplantation-evolution of a revolution

In the 1990s, neonates born with severe congenital heart disease faced more than 50% mortality awaiting an ABO-compatible (ABOc) transplant donor. This desperate situation, together with knowledge of gaps in the adaptive immune system in early childhood, led to the clinical exploration of intentional ABO-incompatible (ABOi) heart transplantation. In 2001, West et al. reported the first series of 10 infants in Canada. Since then, consideration of ABOi heart donors has become the standard of care for children awaiting transplantation in the first few years of life, resulting in reduced wait times and better organ utilization with noninferior post-transplant outcomes compared to ABOc recipients. This state-of-the-art review discusses the clinical development and evolution, underlying and resulting immunological aspects, current challenges, and future directions of ABOi heart transplantation.

Impact of the Pediatric ABO Policy Change on Listings, Transplants, and Outcomes for Children Younger Than 2 Years Listed for Heart Transplantation in the United States

BACKGROUND

We assessed the impact of the liberalized ABO pediatric policy change on candidate characteristics and outcomes for children undergoing heart transplant (HT).

METHODS AND RESULTS

Children <2 years undergoing HT with ABO strategy reported at listing and HT from December 2011 to November 2020 to the Scientific Registry of Transplant Recipients database were included. Characteristics at listing, HT, and outcomes during the waitlist and post-transplant were compared before the policy change (December 16, 2011 to July 6, 2016), and after the policy change (July 7, 2016 to November 30, 2020). The percentage of ABO-incompatible (ABOi) listings did not increase immediately after the policy change (P = .93); however, ABOi transplants increased by 18% (P < .0001). At listing, both before and after the policy change, ABOi candidates had higher urgency status, renal dysfunction, lower albumin, and required more cardiac support (intravenous inotropes, mechanical ventilation) than those listed ABO compatible (ABOc). On multivariable analysis, there were no differences in waitlist mortality between children listed as ABOi and ABOc before the policy change (adjusted hazard ratio [aHR] 0.80, 95% confidence interval [CI] 0.61-1.05, P = .10) or after the policy change (aHR 1.2, 95% CI 0.85-1.6, P = .33). Post-transplant graft survival was worse for ABOi transplanted children before the policy change (aHR 1.8, 95% CI 1.1-2.8, P = .014), but not significantly different after the policy change (aHR 0.94, 95% CI 0.61-1.4, P = .76). After the policy change, ABOi listed children had significantly shorter waitlist times (P < .05).

CONCLUSIONS

The recent pediatric ABO policy change has significantly increased the percentage of ABOi transplantations and decreased waitlist times for children listed ABOi. This change in policy has resulted in broader applicability and actual performance of ABOi transplantation with equal access to ABOi or ABOc organs, and thus eliminated the potential disadvantage of only secondary allocation to ABOi recipients.

Postoperative Outcomes in Infants Undergoing ABO-incompatible Heart Transplantation in the United States

BACKGROUND

ABO-incompatible heart transplant is a method to increase the infant donor pool. However data on long-term survival and rejection after ABO-incompatible heart transplant in recent era are limited.

METHODS

The United Network for Organ Sharing database was queried for infant heart transplants performed from January 2008 to March 2020. Patient demographics and known risk factors for posttransplant mortality were collected. Statistical analysis using Bayesian additive regression trees was performed to evaluate the association of ABO incompatibility and overall survival, graft survival, acute rejection episodes, and length of stay.

RESULTS

Of 1368 included infants (age < 1 year), 280 (20.47%) were ABO incompatible. ABO incompatibility was not associated with increased all-cause mortality, acute rejection episodes, or length of stay, whereas extracorporeal membrane oxygenation and intubation status of the recipient at the time of transplantation were associated with increased all-cause mortality and graft failure. Idiopathic cardiomyopathy was associated with a decreased likelihood of posttransplant all-cause mortality. One-, 5-, and 10-year survival rates among compatible vs incompatible transplants were estimated to be 90% vs 88%, 82% vs 79%, and 77% vs 73%, respectively.

CONCLUSIONS

ABO-incompatible infant heart transplant does not affect posttransplant survival, incidence of rejection, or postoperative length of stay. Therefore it remains a viable and important strategy to increase the infant donor pool.

Rehabilitation in Pediatric Heart Failure and Heart Transplant

Survival of pediatric patients with heart failure has improved due to medical and surgical advances over the past decades. The complexity of pediatric heart transplant patients has increased as medical and surgical management for patients with congenital heart disease continues to improve. Quality of life in patients with heart failure and transplant might be affected by the impact on functional status that heart failure, heart failure complications or treatment might have. Functional areas affected might be motor, exercise capacity, feeding, speech and/or cognition. The goal of rehabilitation is to enhance and restore functional ability and quality of life to those with physical impairments or disabilities. Some of these rehabilitation interventions such as exercise training have been extensively evaluated in adults with heart failure. Literature in the pediatric population is limited yet promising. The use of additional rehabilitation interventions geared toward specific complications experienced by patients with heart failure or heart transplant are potentially helpful. The use of individualized multidisciplinary rehabilitation program that includes medical management, rehabilitation equipment and the use of physical, occupational, speech and feeding therapies can help improve the quality of life of patients with heart failure and transplant.

Clinical outcomes of children receiving ABO-incompatible versus ABO-compatible heart transplantation: a multicentre cohort study

BACKGROUND

ABO-incompatible heart transplantation increases donor availability in young children and is evolving into standard of care in children younger than 2 years. Previous smaller studies suggest similar outcomes to ABO-compatible heart transplantation, but persisting alterations of the immune system in ABO-incompatible recipients might increase the risk of some infections or benefit the graft owing to reduced HLA reactivity. We aimed to assess long-term outcomes in young children after they received ABO-incompatible or ABO-compatible heart transplantation.

METHODS

In this multicentre, prospective cohort study, we analysed data from the Pediatric Heart Transplant Society registry to compare children who received ABO-incompatible or ABO-compatible heart transplantation before age 2 years between Jan 1, 1999, and June 30, 2018. Given significantly different clinical demographics between the two groups, we also matched each ABO-incompatible recipient to two ABO-compatible recipients using propensity score matching. We assessed patient and graft survival, coronary allograft vasculopathy, malignancy, acute rejection (any episode resulting in augmentation of immunosuppression), and infections (requiring intravenous antibiotic or antiviral therapy or life-threatening infections treated with oral therapy).

FINDINGS

We included 2206 children who received a heart transplant before age 2 years, with 11 332·6 patient-years of cumulative observation time. Children who received an ABO-incompatible transplant (n=364) were younger and a larger proportion had congenital heart disease and ventilator and mechanical circulatory support than the ABO-compatible recipients (n=1842). After matching, only differences in blood group (more O in ABO-incompatible and more AB in ABO-compatible groups) and use of polyclonal induction therapy with anti-thymocyte globulins persisted. The two matched groups had similar post-transplantation graft survival (p=0·74), freedom from coronary allograft vasculopathy (p=0·75), and malignancy (p=0·51). ABO-incompatible recipients showed longer freedom from rejection (p=0·0021) in the overall cohort, but not after matching (p=0·48). Severe infections (p=0·0007), bacterial infections (p=0·0005), and infections with polysaccharide encapsulated bacteria (p=0·0005) that share immunological properties with blood group antigens occurred less frequently after ABO-incompatible heart transplantation.

INTERPRETATION

ABO-incompatible heart transplantation for children younger than 2 years is a clinically safe approach, with similar survival and incidences of rejection, coronary allograft vasculopathy, and malignancy to ABO-compatible recipients, despite higher-risk pre-transplant profiles. ABO-incompatible transplantation was associated with less bacterial infection, particularly encapsulated bacteria, suggesting that the acquired immunological changes accompanying ABO tolerance might benefit rather than jeopardise transplanted children.

FUNDING

Pediatric Heart Transplant Society.

Pediatric cardiac waitlist mortality-Still too high

Cardiac transplantation for children with end-stage cardiac disease with no other medical or surgical options is now standard. The number of children in need of cardiac transplant continues to exceed the number of donors considered "acceptable." Therefore, there is an urgent need to understand which recipients are in greatest need of transplant before becoming "too ill" and which "marginal" donors are acceptable in order to reduce waitlist mortality. This article reviewed primarily pediatric studies reported over the last 15 years on waitlist mortality around the world for the various subgroups of children awaiting heart transplant and discusses strategies to try to reduce the cardiac waitlist mortality.

Primary Transplantation for Congenital Heart Disease in the Neonatal Period: Long-term Outcomes

BACKGROUND

Primary transplantation was developed in the 1980s as an alternative therapy to palliative reconstruction of uncorrectable congenital heart disease. Although transplantation achieved more favorable results, its utilization has been limited by the availability of donor organs. This review examines the long-term outcomes of heart transplantation in neonates at our institution.

METHODS

The institutional pediatric heart transplant database was queried for all neonatal heart transplants performed between 1985 and 2017. Follow-up was obtained from medical records and an annually administered questionnaire. Overall survival and time to development of complications were estimated using the Kaplan Meier method. Univariate and multivariate analyses were performed to identify independent predictors of survival.

RESULTS

Heart transplantation was performed in 104 neonates. Median age was 17 days. Hypoplastic left heart syndrome (classic or variant) was the primary diagnosis in 77.8% of patients. Survival at 10 years and 25 years was 73.9% and 55.8%, respectively. At 20 years, freedom from allograft vasculopathy and lymphoproliferative disease was 72.0% and 81.9%, respectively. Freedom from re-transplantation was 81.4% at 20 years. Eight patients (7.6%) developed end-stage renal disease. By multivariate analysis, lower glomerular filtration rate and allograft vasculopathy were the only significant predictors of death.

CONCLUSIONS

Neonatal heart transplantation remains a durable therapy with very acceptable long-term survival. Children transplanted in the newborn period have the potential to reach adulthood with minimal need for reintervention.

The Case for Cardiac Xenotransplantation in Neonates: Is Now the Time to Reconsider Xenotransplantation for Hypoplastic Left Heart Syndrome?

Neonatal cardiac transplantation for hypoplastic left heart syndrome (HLHS) is associated with excellent long-term survival compared to older recipients. However, heart transplantation for neonates is greatly limited by the critical shortage of donor hearts, and by the associated mortality of the long pre-transplant waiting period. This led to the development of staged surgical palliation as the first-line surgical therapy for HLHS. Recent advances in genetic engineering and xenotransplantation have provided the potential to replicate the excellent results of neonatal cardiac allotransplantation while eliminating wait-list-associated mortality through genetically modified pig-to-human neonatal cardiac xenotransplantation. The elimination of the major pig antigens in addition to the immature B-cell response in neonates allows for the potential to induce B-cell tolerance. Additionally, the relatively mature neonatal T-cell response could be reduced by thymectomy at the time of operation combined with donor-specific pig thymus transplantation to "reprogram" the host's T-cells to recognize the xenograft as host tissue. In light of the recent significantly increased graft survival of genetically-engineered pig-to-baboon cardiac xenotransplantation, we propose that now is the time to consider devoting research to advance the potential clinical application of cardiac xenotransplantation as a treatment option for patients with HLHS. Employing cardiac xenotransplantation could revolutionize therapy for complex congenital heart defects and open a new chapter in the field of pediatric cardiac transplantation.

An approach to induction of tolerance to pig cardiac xenografts in neonates

There is a continuing need for donor hearts for infants with complex congenital heart defects. The transplantation of hearts from neonatal pigs would be an alternative to human organs, particularly if donor-specific immunological tolerance could be achieved. The great majority of infant humans do not make natural (preformed) antibodies against triple-knockout (TKO) pigs (that do not express any of the three known pig antigens against which humans have natural anti-pig antibodies). The transplantation of a heart from a TKO pig into an infant would therefore minimize any risk of early antibody-mediated rejection, and, with adequate immunosuppressive therapy, prolonged graft survival may well be achieved. Total host thymectomy (commonly carried out at the time of orthotopic heart transplantation in this age group) ± residual T-cell depletion and donor-specific pig thymus tissue transplantation might induce T-cell tolerance and allow immunosuppressive therapy to be discontinued (if there is in vitro evidence of T-cell and B-cell nonresponsiveness to donor-specific pig cells). Even if tolerance were not achieved, with continuing immunosuppressive therapy, the graft would likely "bridge" the patient until a suitable allograft became available or be associated with prolonged xenograft function.

Improved Survival While Waiting and Risk Factors for Death in Pediatric Patients Listed for Cardiac Transplantation

Our aim is to determine (a) the effect of changes in pre-transplant management and era of listing on survival of children listed for HTx and (b) risk factors for death while waiting. This retrospective study included all children listed between 1/1993 and 12/2009 at our center. Survival was determined using survival analysis and competing outcomes modeling. There were 254 listed patients of whom 144 (57%) had congenital heart disease, 208 (82%) were status 1, 52 used ECMO (20%), and 28 used ventricular assist device support (VAD) (11%) beginning in 2005. Overall mortality while waiting was 17% at 6 months, and 69% underwent transplant. Seven of 95 patients (7%) died waiting after 2004 compared to 36 of 159 (23%) before. ECMO and earlier year of listing were significant risk factors (p < 0.001) for wait-list mortality, whereas mortality was significantly lower (p = 0.002) after availability of VADs. Race, gender, blood type, and congenital diagnosis were not significant risk factors for death. Survival in pediatric patients listed for HTx has improved significantly in the current era at our institution. The availability of pediatric VADs has had a significant impact on survival while waiting in children listed for transplantation.

A contemporary review of paediatric heart transplantation and mechanical circulatory support

Improvements in the care of children with cardiomyopathy, CHDs, and acquired heart disease have led to an increased number of children surviving with advanced heart failure. In addition, the advent of more durable mechanical circulatory support options in children has changed the outcome for many patients who otherwise would have succumbed while waiting for heart transplantation. As a result, more children with end-stage heart failure are being referred for heart transplantation, and there is increased demand for a limited donor organ supply. A review of important publications in the recent years related to paediatric heart failure, transplantation, and mechanical circulatory support show a trend towards pushing the limits of the current therapies to address the needs of this growing population. There have been a number of publications focussing on previously published risk factors perceived as barriers to successful heart transplantation, including elevated pulmonary vascular resistance, medication non-adherence, re-transplantation, transplantation of the failed Fontan patient, and transplantation in an infant or child bridged with mechanical circulatory support. This review will highlight some of these key articles from the last 3 years and describe recent advances in the understanding, diagnosis, and management of children with end-stage heart disease.

ABH-Glycan Microarray Characterizes ABO Subtype Antibodies: Fine Specificity of Immune Tolerance After ABO-Incompatible Transplantation

Organ transplantation from ABO blood group-incompatible (ABOi) donors requires accurate detection, effective removal and subsequent surveillance of antidonor antibodies. Because ABH antigen subtypes are expressed differently in various cells and organs, measurement of antibodies specific for the antigen subtypes in the graft is essential. Erythrocyte agglutination, the century-old assay used clinically, does not discriminate subtype-specific ABO antibodies and provides limited information on antibody isotypes. We designed and created an ABO-glycan microarray and demonstrated the precise assessment of both the presence and, importantly, the absence of donor-specific antibodies in an international study of pediatric heart transplant patients. Specific IgM, IgG, and IgA isotype antibodies to nonself ABH subtypes were detected in control participants and recipients of ABO-compatible transplants. Conversely, in children who received ABOi transplants, antibodies specific for A subtype II and/or B subtype II antigens-the only ABH antigen subtypes expressed in heart tissue-were absent, demonstrating the fine specificity of B cell tolerance to donor/graft blood group antigens. In contrast to the hemagglutination assay, the ABO-glycan microarray allows detailed characterization of donor-specific antibodies necessary for effective transplant management, representing a major step forward in precise ABO antibody detection.

Transplant Tolerance Induction in Newborn Infants: Mechanisms, Advantages, and Potential Strategies

Although several tolerance induction protocols have been successfully implemented in adult renal transplantation, no tolerance induction approach has, as yet, been defined for solid organ transplantations in young infants. Pediatric transplant recipients have a pressing demand for the elaboration of tolerance induction regimens. Indeed, since they display a longer survival time, they are exposed to a higher level of risks linked to long-term immunosuppression (IS) and to chronic rejection. Interestingly, central tolerance induction may be of great interest in newborns, because of their immunological immaturity and the important role of the thymus at this early stage in life. The present review aims to clarify mechanisms and strategies of tolerance induction in these immunologically premature recipients. We first introduce the discovery and mechanisms of neonatal tolerance in murine experimental models and subsequently analyze tolerance induction in human newborn infants. Hematopoietic mixed chimerism in neonates is also discussed based on in utero hematopoietic stem cell (HSC) transplant studies. Then, we review the recent advances in tolerance induction approaches in adults, including the infusion of HSCs associated with less toxic conditioning regimens, regulatory T cells/facilitating cells/mesenchymal stem cells transplantation, costimulatory blockade, and thymus manipulation. Finally, IS withdrawal in pediatric solid organ transplant is discussed. In conclusion, the establishment of transplant tolerance induction in infants is promising and deserves further investigations. Future studies could focus on the selection of patients, on less toxic conditioning regimens, and on biomarkers for IS minimization or withdrawal.

Emerging science in paediatric heart transplantation: donor allocation, biomarkers, and the quest for evidence-based medicine

Heart transplantation offers excellent survival benefit to children with end-stage heart failure. With its success, the number of potential recipients continues to exceed the number of available donors. Developing strategies to safely increase donor utilisation is crucial to decreasing wait-list mortality. A new paediatric heart allocation policy is set to be implemented with the goal of prioritising the most urgent listed candidates. Owing to excellent outcomes of ABO-incompatible heart transplantation, the sickest infants will soon receive priority for heart offers irrespective of blood group. Allosensitisation poses unique challenges within the paediatric population; ongoing multi-centre studies are poised to refine our understanding of key risk factors and optimal treatment strategies. Biomarkers for acute cellular rejection, such as donor-specific cell-free DNA, and cardiac allograft vasculopathy, such as VEGF-A, may lead to a decreased need for invasive screening. Ultimately, well-designed and executed randomised control trials of post-transplant immunosuppression are required to improve long-term outcomes after paediatric heart transplantation.

ABO blood group antibody levels in infants exposed to mechanical circulatory support

ABO sensitization is a barrier to ABO-incompatible heart transplantation in infants. We investigate the development of ABO antibodies in infants with and without mechanical circulatory support (MCS) during their waiting period. Although the proportion of patients with antibodies was similar between the groups, the median age at antibody detection was only 9 days (6-198) for MCS vs. 223 days (28-367) for non-MCS patients (P = 0.028), suggesting MCS is associated with earlier ABO antibody detection.

Pediatric heart transplantation-indications and outcomes in the current era

Pediatric heart transplantation (HTx) remains an important treatment option in the care of children with end-stage heart disease, whether it is secondary to cardiomyopathy or congenital heart disease (CHD). As surgical outcomes for CHD have improved, the indications for pediatric HTx have had to be dynamic, not only for children with CHD but also for the growing population of adults with CHD. As the field of pediatric HTx has evolved, the outcomes for children undergoing HTx have improved. This is undoubtedly due to the continued research efforts of both single-center studies, as well as research collaboratives such as the International Society for Heart and Lung Transplantation (ISHLT) and the Pediatric Heart Transplant Study (PHTS) group. Research collaboratives are increasingly important in pediatric HTx as single center studies for a limited patient population may not elicit strong enough evidence for practice evolution. Similarly, complications that limit the long term graft survival may occur in a minority of patients thus pooled experience is essential. This review focuses on the indications and outcomes for pediatric HTx, with a special emphasis on studies generated by these research collaboratives.

Pediatric heart transplantation-indications and outcomes in the current era

Pediatric heart transplantation (HTx) remains an important treatment option in the care of children with end-stage heart disease, whether it is secondary to cardiomyopathy or congenital heart disease (CHD). As surgical outcomes for CHD have improved, the indications for pediatric HTx have had to be dynamic, not only for children with CHD but also for the growing population of adults with CHD. As the field of pediatric HTx has evolved, the outcomes for children undergoing HTx have improved. This is undoubtedly due to the continued research efforts of both single-center studies, as well as research collaboratives such as the International Society for Heart and Lung Transplantation (ISHLT) and the Pediatric Heart Transplant Study (PHTS) group. Research collaboratives are increasingly important in pediatric HTx as single center studies for a limited patient population may not elicit strong enough evidence for practice evolution. Similarly, complications that limit the long term graft survival may occur in a minority of patients thus pooled experience is essential. This review focuses on the indications and outcomes for pediatric HTx, with a special emphasis on studies generated by these research collaboratives.

C3d plasma levels and CD21 expressing B-cells in children after ABO-incompatible heart transplantation: Alterations associated with blood group tolerance

BACKGROUND

Most children transplanted with ABO-incompatible (ABOi) hearts develop selective tolerance to donor A/B antigens, whereas anti-A/B antibodies typically re-accumulate in adults after ABOi kidney transplantation. Deficiency of essential factors linking innate and adaptive immunity in early childhood may promote development of tolerance, specifically interactions between complement split product C3d and its ligand CD21 on B cells, considering their role in augmenting "T-independent" B-cell activation.

METHODS

Blood and clinical data were analyzed from children after ABOi or ABO-compatible (ABOc) heart transplantation (HTx). Plasma C3d levels were quantified by enzyme-linked immunoassay. Peripheral blood mononuclear cells (PBMC) were phenotyped by flow cytometry; expression of B-cell co-receptor components CD21 and CD81 was quantified.

RESULTS

Fifty-five samples from pediatric HTx recipients (median age at transplant: 4.2 [range 0.03 to 20.4] months; age at sample collection: 14.6 [0.04 to 51.3] months; 53% ABOi) and 21 controls were studied. CD21-expressing B cells increased in trend with age (p = 0.079); longitudinal measures in individual patients showed a strong correlation with age. CD21 expression intensity in B-cells was not age-dependent. Plasma C3d levels did not correlate with age. Comparing ABOc vs ABOi HTx, CD21-expressing cell proportions were similar; however, serum C3d levels were significantly lower after ABOi HTx (p < 0.05).

CONCLUSIONS

In children, including HTx patients, CD21-expressing B-cells show a trend to increase with age, corresponding with improved responsiveness to polysaccharide antigens. This does not differ in patients with ABOi grafts developing tolerance to donor ABO antigens. C3d levels are not age-dependent, but reduced C3d levels after ABOi HTx suggest altered complement metabolism contributing to ABO tolerance.

Lung and heart allocation in the United States

Lung and heart allocation in the United States has evolved over the past 20-30 years to better serve transplant candidates and improve organ utilization. The current lung allocation policy, based on the Lung Allocation Score, attempts to take into account risk of death on the waiting list and chance of survival posttransplant. This policy is flexible and can be adjusted to improve the predictive ability of the score. Similarly, in response to the changing clinical phenotype of heart transplant candidates, heart allocation policies have evolved to a multitiered algorithm that attempts to prioritize organs to the most infirm, a designation that fluctuates with trends in therapy. The Organ Procurement and Transplantation Network and its committees have been responsive, as demonstrated by recent modifications to pediatric heart allocation and mechanical circulatory support policies and by ongoing efforts to ensure that heart allocation policies are equitable and current. Here we examine the development of US lung and heart allocation policy, evaluate the application of the current policy on clinical practice and explore future directions for lung and heart allocation.

Using the UNOS/SRTR and PHTS Databases to Improve Quality in Pediatric Cardiac Transplantation

Data collection and dissemination have been a part of the US transplant experience since its earliest days. As part of this process, the United Network for Organ Sharing (UNOS) has provided open access to its data. In addition, multiinstitutional groups such as the Pediatric Heart Transplant Study (PHTS) have collected data of particular interest to pediatric and congenital transplants. This wealth of data enables quality improvement along several pathways including individual program assessment and improvement and development of both structure and process measures for ongoing improvement. Extensive literature exists utilizing these data, but must be read critically, recognizing the limitations presented by missing variables (whether uncollected or collected but left blank), reproducibility, and small sample sizes among pediatric patients. However, despite these limitations, opportunity continues to exist to apply these data sets to ongoing questions of quality and optimize organ allocation and long-term survival among pediatric patients with heart failure.

Incompatible ABO-plasma exchange and its impact on patient selection in paediatric cardiac transplantation

OBJECTIVES

A decade ago, the first series of ABO-incompatible heart transplants was published, with surprising and extremely promising results; drastically reduced waiting list mortalities of infants listed for heart transplantation. Essential to the procedure was the process of plasma exchange transfusion, required to reduce isohaemagglutinin titres and facilitate the crossing of ABO blood group boundaries. Since then, Great Ormond Street Hospital, London has offered ABO-incompatible heart transplants to infants who potentially would die waiting for a suitable organ. We report the results of a decade of evolving plasma exchange experience and its impact upon patient selection.

METHODS

A retrospective analysis was undertaken of all elective ABO-incompatible heart transplants at Great Ormond Street Children's Hospital from January 2001 until January 2011. Data were sought on underlying conditions and demographics of the patients, the isohaemagglutinin titre before and after plasma exchange and survival figures to date.

RESULTS

Twenty-one patients underwent ABO-incompatible heart transplantation, ranging from 3 to 44 months, with preoperative isohaemagglutinin titres ranging from 0 to 1:32. All patients underwent a "3 times" plasma exchange before transplantation, requiring exchange volumes of up to 3209 mL. Postoperative isohaemagglutinin titres ranged from 0 to 1:16. One patient died of causes unrelated to organ rejection.

CONCLUSIONS

Our data showed that eight patients (38.1%) were older than the previously suggested 12-month cut-off age. Using a combination of adult reservoir/paediatric oxygenator and extracorporeal circuit, ABO-incompatible plasma exchange transfusions can be undertaken safely using a simplified '3 times' method, reducing the circulating levels of isohaemagglutinins whilst providing minimal circuit size. This allows ABO-incompatible heart transplantation in a broader patient population than previously reported.

Pushing the boundaries: the current status of ABO-incompatible cardiac transplantation

Since the introduction of intentional ABO-incompatible (ABOi) cardiac transplantation in infants in the late 1990's, the number of patients listed for and undergoing ABOi transplants has increased. This practice has been shown to lead to a reduction in waiting list mortality and increased utilisation of donor organs with equivalent outcomes to ABO-compatible transplants. Differences in the infant immune system provide a window of opportunity for ABOi transplantation. However it is increasingly clear that older patients and those with significant amounts of blood group antibody specific isohaemagglutinins may also benefit. Newer research is now focussing on longer term outcomes of ABOi transplants - in particular the development of graft accommodation or tolerance. This review assesses the current status of ABO-incompatible cardiac transplantation both in infants and in sensitized and older patients.

ABO-incompatible heart transplantation: analysis of the Pediatric Heart Transplant Study (PHTS) database

BACKGROUND

ABO incompatible (ABOi) heart transplantation is an accepted approach to increasing organ availability for young patients. Previous studies have suggested that early survival for ABOi transplants is similar to ABO compatible (ABOc) transplants. We analyzed the Pediatric Heart Transplant Study (PHTS) database from 1/96 to 12/08 to further assess this strategy.

METHODS

We analyzed the numbers of ABOi and ABOc done at the PHTS centers. We then compared the clinical characteristics, and short-term freedom from death, rejection and infection in the ABOi patients with the patients that had an ABOc heart transplant during the same period. All patients were less than or equal to 15 months of age at listing (the age of the oldest ABOi patient). We adjusted for co-variates shown to increase risk for mortality (age less than 1 month, extracorporeal membrane oxygenation (ECMO), ventilator, previous sternotomy, and congenital heart disease).

RESULTS

There were 931 total transplants done at 34 PHTS centers during the 12 year time period in patients ≤15 months of age. Of these, 502 transplants were performed at 20 PHTS centers that did at least one ABOi heart transplant. Eighty-five of the 502 (17%) were ABOi. At time of transplant, ABOi recipients compared with ABOc were more likely to be on a ventilator (49.4% vs 36.5%, p=0.025), and more often supported with ECMO (23.5% vs 13.4%, p=0.018). There was similar survival at 12 months (82% vs 84%, p=0.7). In risk adjusted analysis ABOi status was not associated with 1 year mortality (HR 0.85, 95% CI 0.45-1.6, p=0.61). The ABOi patients had greater freedom from rejection when compared with ABOc patients for all 34 centers (75% vs 62%, p=0.016), but the difference was not significant when limited only to the 20 centers doing ABOi transplants (75% vs 69%, p=0.4). The ABOi cohort had lower infection rates (23.5% vs 37.9%, p = 0.013). This difference remained after adjusting for center and other covariates.

CONCLUSIONS

In center and risk adjusted analysis, young children who received an ABOi transplant had equivalent one-year survival and freedom from rejection compared with those who received an ABOc transplant. In spite of the favorable outcome for ABOi recipients, many centers appear to reserve ABOi transplantation for sicker patients. These data mandate reexamination of the current United Network for Organ Sharing (UNOS) policy that gives priority to ABOc over ABOi transplantation in the United States.

ABO-incompatible hearts for infant transplantation

PURPOSE OF REVIEW

The practice of offering ABO-incompatible (ABOi) heart transplantation during infancy was initiated based on the rationale that infants are at the highest risk of dying while waiting for a transplant, yet are at low risk of hyperacute antibody-mediated rejection due to immunologic immaturity. Since the first report of intentional ABOi heart transplantation a decade ago, its success has been corroborated in numerous reports and the practice has been widely adopted. This review summarizes clinical results in reports of ABOi transplantation and the evolution of ABOi listing strategies, as well as evidence of immune tolerance after ABOi transplantation.

RECENT FINDINGS

Recent reports have documented comparable midterm and long-term clinical outcomes in ABOi and ABO-compatible (ABOc) heart transplant recipients in terms of survival and posttransplant complications. Despite successful outcomes, however, there are obstacles to widespread implementation of ABOi transplantation in the USA and in some European centers. The notable deficiency in development of antibody production to donor A/B antigens following ABOi transplantation described in early reports has been corroborated, with some exceptions. Potential advantages of ABOi transplantation are emerging as well as innovative strategies that may allow ABOi heart transplantation beyond the age of infancy.

SUMMARY

ABOi heart transplantation is one example in which immunologic immaturity has been exploited to the advantage of pediatric transplant recipients. In-depth exploration of transplant-related immunobiology in the young may reveal further opportunities.

Trends in wait-list mortality in children listed for heart transplantation in the United States: era effect across racial/ethnic groups

We sought to evaluate trends in overall and race-specific pediatric heart transplant (HT) wait-list mortality in the United States (US) during the last 20 years. We identified all children <18 years old listed for primary HT in the US during 1989-2009 (N = 8096, 62% White, 19% Black, 13% Hispanic and 6% Other) using the Organ Procurement and Transplant Network database. Wait-list mortality was assessed in four successive eras (1989-1994, 1995-1999, 2000-2004 and 2005-2009). Overall wait-list mortality declined in successive eras (26%, 23%, 18% and 13%, respectively). The decline across eras remained significant in adjusted analysis (hazard ratio [HR] 0.70 in successive eras, 95% confidence interval [CI], 0.67-0.74) and was 67% lower for children listed during 2005-2009 versus those listed during 1989-1994 (HR 0.33; CI, 0.28-0.39). In models stratified by race, wait-list mortality decreased in all racial groups in successive eras. In models stratified by era, minority children were not at higher risk of wait-list mortality in the most recent era. We conclude that the risk of wait-list mortality among US children listed for HT has decreased by two-thirds during the last 20 years. Racial gaps in wait-list mortality present variably in the past are not present in the current era.

Circulation: Heart Failure's Editors' Picks: Most Important Papers in Epidemiology and Outcomes

The following are highlights from the new series, Circulation: Heart Failure Topic Review. This series will summarize the most important manuscripts, as selected by the editors, which have published in the Circulation portfolio. The objective of this new series is to provide our readership with a timely and comprehensive selection of important papers that are relevant to the heart failure audience, covering a variety of areas within the heart failure field. The studies included in this article represent the most noteworthy research in the areas of epidemiology and outcomes.

Extended donors in liver transplantation

Several criteria are used to differentiate between standard and extended allograft donors. These criteria include deceased after cardiac death, advanced donor age, steatosis, previous malignancy in the donor, hepatitis C virus-positive allografts, human T-cell lymphotropic virus-positive allografts, active infections in the donor, high-risk donors, split liver transplantations, and living donor liver transplantations. Review of the literature can lead each practitioner to incorporate extended criteria donors into their transplant program, thereby individualizing the use of these allografts, increasing the donor pool, and decreasing overall waitlist mortality.

Humoral immunity and antibody-mediated rejection in solid organ transplantation

The humoral arm of the immune system provides robust protection against extracellular pathogens via the production of antibody molecules that neutralize or facilitate the destruction of microorganisms. However, the humoral immune system also provides a significant barrier to solid organ transplantation due to the antibody-mediated recognition of non-self proteins and carbohydrates expressed on transplanted organs. Historically, the presence of donor-specific antibodies (DSA) that recognize donor HLA molecules, incompatible ABO blood group antigens and other endothelial or xenogeneic antigens was considered a contraindication to transplantation. However, recent advances in antibody testing and immunosuppressive therapies have made it possible to cross certain antibody barriers successfully. In this article, we review our current understanding of antibody-mediated processes in solid organ transplantation and discuss the clinically available treatment options for preventing and treating antibody-mediated rejection.

Heart transplantation for congenital heart disease in the first year of life

Successful infant heart transplantation has now been performed for over 25 years. Assessment of long term outcomes is now possible. We report clinical outcomes for322 patients who received their heart transplant during infancy. Actuarial graft survival for newborn recipients is 59% at 25 years. Survival has improved in the most recent era. Cardiac allograft vasculopathy is the most important late cause of death with an actuarial incidence at 25 years of 35%. Post-transplant lymphoma is estimated to occur in 20% of infant recipients by25 years. Chronic kidney disease grade 3 or worse is present in 31% of survivors. The epidemiology of infant heart transplantation has changed through the years as the results for staged repair improved and donor resources remained stagnant. Most centers now employ staged repair for hypoplastic left heart syndrome and similar extreme forms of congenital heart disease. Techniques for staged repair, including the hybrid procedure, are described. The lack of donors is described with particular note regarding decreased donors due to newer programs for appropriate infant sleep positioning and infant car seats. ABO incompatible donors are a newer resource for maximizing donor resources, as is donation after circulatory determination of death and techniques to properly utilize more donors by expanding the criteria for what is an acceptable donor. An immunological advantage for the youngest recipients has long been postulated, and evaluation of this phenomenon may provide clues to the development of accommodation and/or tolerance.