Humoral Rejection in Pediatric Orthotopic Heart Transplantation

DQB1 antigen matching improves rejection-free survival in pediatric heart transplant recipients

BACKGROUND

Presence of donor-specific antibodies (DSAs), particularly to class II antigens, remains a major challenge in pediatric heart transplantation. Donor-recipient human leukocyte antigen (HLA) matching is a potential strategy to mitigate poor outcomes associated with DSAs. We evaluated the hypothesis that antigen mismatching at the DQB1 locus is associated with worse rejection-free survival.

METHODS

Data were collected from Scientific Registry of Transplant Recipients for all pediatric heart transplant recipients 2010-2021. Only transplants with complete HLA typing at the DQB1 locus for recipient and donor were included. Primary outcome was rejection-free graft survival through 5 years.

RESULTS

Of 5,115 children, 4,135 had complete DQB1 typing and were included. Of those, 503 (12%) had 0 DQB1 donor-recipient mismatches, 2,203 (53%) had 1, and 1,429 (35%) had 2. Rejection-free survival through 5 years trended higher for children with 0 DQB1 mismatches (68%), compared to those with 1 (62%) or 2 (63%) mismatches (pairwise p = 0.08 for both). In multivariable analysis, 0 DQB1 mismatches remained significantly associated with improved rejection-free graft survival compared to 2 mismatches, while 1 DQB1 mismatch was not. Subgroup analysis showed the strongest effect in non-Hispanic Black children and those undergoing retransplant.

CONCLUSIONS

Matching at the DQB1 locus is associated with improved rejection-free survival after pediatric heart transplant, particularly in Black children, and those undergoing retransplant. Assessing high-resolution donor typing at the time of allocation may further corroborate and refine this association. DQB1 matching may improve long-term outcomes in children stabilized either with optimal pharmacotherapy or supported with durable devices able to await ideal donors.

Modifications to therapeutic plasma exchange to achieve rapid exchange on cardiopulmonary bypass prior to pediatric cardiac transplant

BACKGROUND

Cardiac transplants increasingly occur following placement of ventricular assist devices (VADs). A strong association exists between human leukocyte antigen (HLA) sensitization and VAD placement; however, desensitization protocols that utilize therapeutic plasma exchange (TPE) are fraught with technical challenges and are at increased risk of adverse events. In response to increased VAD utilization in our pre-transplant population, we developed a new institutional standard for TPE in the operating room.

METHODS

Through a multidisciplinary effort, we developed an institutional protocol for intraoperative TPE immediately prior to cardiac transplantation after cannulation onto cardiopulmonary bypass (CPB). All procedures used the standard TPE protocol on the Terumo Optia (Terumo BCT, Lakewood, CO, USA), but incorporated multiple modifications to limit patients' bypass times, and to coordinate with the surgical teams. These modifications included deliberate misidentification of replacement fluid and maximization of the citrate infusion rate.

RESULTS

These adjustments allowed the machine to run at maximal inlet speeds, minimizing duration of TPE. To date, 11 patients have been treated with this protocol. All survived their cardiac transplantation operation. Hypocalcemia and hypotension were noted; however, none of these adverse events appeared to have clinical impact. Technical complications included unexpected fibrin deposition in the TPE circuit and air in the inlet line due to surgical manipulation of the CPB cannula. No thromboembolic complications occurred in any patient.

CONCLUSION

We feel that this procedure can be rapidly and safely performed in HLA sensitized pediatric patients on CPB to limit the risk of antibody mediated rejection of their heart transplant.

Antibodies to human leukocyte antigens and their association with blood product exposures in pediatric patients undergoing cardiac transplantation

BACKGROUND AND AIMS

Previous blood product exposures may result in the development of antibodies to human leukocyte antigens (HLA). Pediatric heart transplant recipients who have these antibodies experience increased morbidity and mortality after transplantation. In this study, our aims were to confirm the association of previous allogeneic blood product exposures with the formation of anti-HLA antibodies, determine which blood components pose the greatest risk of developing antibodies, and assess differences in outcomes after transplantation between patients who had anti-HLA antibodies and those who did not.

METHODS

This retrospective investigation included all children who underwent cardiac transplantation at Children's Healthcare of Atlanta from January 1, 2015 through December 31, 2018. Chart reviews were performed to collect pertinent data. Anti-HLA antibodies were detected by single antigen bead testing. Antibody burden was tabulated using the calculated panel reactive antibody (cPRA) score immediately prior to transplantation. Statistical analyses were conducted to examine differences based on HLA antibody status and identify associations with outcomes of interest.

RESULTS

Our results show a significant association between pretransplant blood product exposures and HLA antibody status. Children with a pretransplant blood product exposure had 7.98 times the odds of developing an anti-HLA antibody compared to those without a pretransplant blood product exposure (p = .01). We also found a significant association between a previous red blood cell (RBC) exposure and HLA antibody status (p = .01) which was not found for other blood component exposures. Patients who were HLA antibody positive were more likely to develop a donor-specific antibody (DSA) after transplantation (p = .04).

CONCLUSIONS

Exposure to previous allogeneic blood products affects the development of anti-HLA antibodies in children presenting for heart transplantation. Previous RBC exposures resulted in HLA antibody positivity more than other blood component exposures. Importantly, the presence of HLA antibodies was associated with the development of DSAs post-transplantation. Developing transfusion strategies to reduce allogeneic blood product exposures in children who may need future cardiac transplantation should be a high priority.

Label-free Identification of Antibody-mediated Rejection in Cardiac Allograft Biopsies Using Infrared Spectroscopic Imaging

BACKGROUND

Antibody-mediated rejection (AMR) in cardiac allograft recipients remains less well-understood than acute cellular rejection, is associated with worse outcomes, and portends a greater risk of developing chronic allograft vasculopathy. Diffuse immunohistochemical C4d staining of capillary endothelia in formalin-fixed, paraffin-embedded right ventricular endomyocardial biopsies is diagnostic of immunopathologic AMR but serves more as a late-stage marker. Infrared (IR) spectroscopy may be a useful tool in earlier detection of rejection. We performed mid-IR spectroscopy to identify a unique biochemical signature for AMR.

METHODS

A total of 30 posttransplant formalin-fixed paraffin-embedded right ventricular tissue biopsies (14 positive for C4d and 16 negative for C4d) and 14 native heart biopsies were sectioned for IR analysis. Infrared images of entire sections were acquired and regions of interest from cardiomyocytes were identified. Extracted spectra were averaged across many pixels within each region of interest. Principal component analysis coupled with linear discriminant analysis and predictive classifiers were applied to the data.

RESULTS

Comparison of averaged mid-IR spectra revealed unique features among C4d-positive, C4d-negative, and native heart biopsies. Principal component analysis coupled with linear discriminant analysis and classification models demonstrated that spectral features from the mid-IR fingerprint region of these 3 groups permitted accurate automated classification into each group.

CONCLUSIONS

In cardiac allograft biopsies with immunopathologic AMR, IR spectroscopy reveals a biochemical signature unique to AMR compared with that of nonrejecting cardiac allografts and native hearts. Future study will focus on the predictive capabilities of this IR signature.

Current Topics and Controversies in Pediatric Heart Transplantation: Proceedings of the Pediatric Heart Transplantation Summit 2017

In October 2017, a pediatric heart transplant summit was held in Seattle-the first of its kind internationally-which focused solely upon controversies in pediatric end-stage heart failure management and pediatric heart transplantation. We selected five of the most popular and contentious topics and asked the speakers to provide a position paper. Worldwide, the vast majority of programs perform only a handful of pediatric heart transplants a year. Because of this, these "orphan" areas of investigation provide an opportunity for us as a community to aggregate our collective knowledge, which may represent the only viable way that we might sort through these complex and controversial issues in the field. We hope this represents the first of many such conferences and that this initial selection of papers encourages us to begin this collaborative process.

Pathological antibody-mediated rejection in pediatric heart transplant recipients: Immunologic risk factors, hemodynamic significance, and outcomes

Biopsy-diagnosed pAMR has been observed in over half of pediatric HT recipients within 6 years of transplantation. We report the incidence and outcomes of pAMR at our center. All endomyocardial biopsies for all HT recipients transplanted between 2010 and 2015 were reviewed and classified using contemporary ISHLT guidelines. Graft dysfunction was defined as a qualitative decrement in systolic function by echocardiogram or an increase of ≥3 mm Hg in atrial filling pressure by direct measurement. Among 96 patients, pAMR2 occurred in 7 (7%) over a median follow-up period of 3.1 years, while no cases of pAMR3 occurred. A history of CHD, DSA at transplant, and elevated filling pressures were associated with pAMR2. Five-sixths (83%) of patients developed new C1q+ DSA at the time of pAMR diagnosis. There was a trend toward reduced survival, with 43% of patients dying within 2.3 years of pAMR diagnosis.

Acute humoral rejection in an infant without risk factors after heart transplantation

Graft rejection is the most common factor that limits graft survival after transplantation. During infancy, the humoral immune system is partially suppressed and humoral rejection of a cardiac allograft has not been reported in the absence of risk factors such as prior transplantation, blood transfusions, ventricular assist devices, and elevation of panel reactive antibodies. We present a case of an infant with dilated cardiomyopathy who developed multiple episodes of acute humoral rejection after heart transplantation in the absence of risk factors.

Outcome of antibody-mediated rejection compared to acute cellular rejection after pediatric heart transplantation

Outcomes of ACR after pediatric HTx have been well described, but less has been reported on outcomes of AMR. We compared the clinical characteristics and cardiovascular outcomes (composite end-point of death, retransplantation, or allograft vasculopathy) of pediatric HTx recipients with AMR, ACR, and no rejection in a retrospective single-center study of 104 recipients. Twenty were treated for AMR; 15 were treated for ACR. Recipients with AMR had an increased frequency of congenital heart disease (90% vs ACR 67% vs no rejection 59%, P = .03), homograft (68% vs 7% vs 18%, P < .001), HLA sensitization (45% vs 13% vs 13%, P = .008), and positive cross-match (30% vs 7% vs 9%, P = .046). AMR caused hemodynamic compromise more often than ACR (39% vs 4%, P = .02). AMR recipients had worse cardiovascular outcome than recipients with ACR or no rejection (40% vs 20% vs 8.6%, P = .003). In bivariate Cox analysis, AMR (HR 4.1, CI 1.4-12.0, P = .009) and ischemic time (HR 1.6, CI 1.1-2.3, P = .02) were associated with worse cardiovascular outcome; ACR was not. In summary, pediatric HTx recipients who develop AMR have worse cardiovascular outcome than recipients who develop only ACR or experience no rejection at all.

Antibody-mediated rejection in the cardiac allograft: diagnosis, treatment and future considerations

PURPOSE OF REVIEW

This review summarizes the latest publications dealing with antibody-mediated rejection (AMR) and defines areas of controversy and future steps that may improve the outcome for patients with this virulent form of rejection.

RECENT FINDINGS

Recent progress includes publication of standardized pathologic criteria for acute AMR by the International Society for Heart and Lung Transplantation (ISHLT) and guidelines for treatment of acute AMR by the American Heart Association, endorsed by ISHLT as well. Recently published review articles emphasize the important role of innate immune mechanisms, clarify the role of viral infection and provide insights into vascular biology and the role of innate effector populations, macrophages and dendritic cells.

SUMMARY

Strategies for future studies are discussed in the context of these new findings and similar efforts undertaken by renal and liver allograft investigators.

Bortezomib use in a pediatric cardiac transplant center

Data are limited on the efficacy and safety of bortezomib for the treatment of AMR following OHT for pediatric acquired or CHD. Retrospective chart review identified patients who received bortezomib for acute (n = 3, within two wk of diagnosis) and chronic (n = 1, three months after diagnosis) AMR or as part of a desensitization regimen (n = 1). Bortezomib was associated with a 3-66% reduction in class I DSA and a 7-82% reduction in class II DSA. Two of the three acute AMR cases resolved by the first follow-up biopsy. Two patients with AMR resolution are currently well. One patient developed a second episode of AMR, which was unresponsive to bortezomib therapy and required retransplantation for progressive coronary allograft vasculopathy. One patient died shortly after the third cycle from multi-organ failure. The desensitization patient showed transient HLA reduction with two cycles, but died five months after transplant from sepsis. Complications included infection (3/5), peripheral neuropathy (2/5), AKI (2/5), and thrombocytopenia (3/5). Adverse events appear more common in critically ill patients. Bortezomib therapy resulted in variable DSA reduction and AMR resolution in AMR in OHT secondary to pediatric acquired or CHD.

Effect of human leukocyte antigen-C and -DQ matching on pediatric heart transplant graft survival

BACKGROUND

A higher degree of human leukocyte antigen (HLA) matching at the A, B, and DR loci has been associated with improved long-term survival after pediatric heart transplantation in multiple International Society for Heart and Lung Transplantation registry reports. The aim of this study was to investigate the association of HLA matching at the C and DQ loci with pediatric graft survival.

METHODS

The United Network of Organ Sharing database was queried for isolated heart transplants that occurred from 1988 to 2012 with a recipient age of 17 or younger and at least 1 postoperative follow-up encounter. When HLA matching at the C or DQ loci were analyzed, only transplants with complete typing of donor and recipient at the respective loci were included. Transplants were divided into patients with at least 1 match at the C locus (C-match) vs no match (C-no), and at least 1 match at the DQ (DQ-match) locus vs no match (DQ-no). Primary outcome was graft loss. Univariate analysis was performed with the log-rank test. Cox regression analysis was performed with the following patient factors included in the model: recipient age, ischemic time; recipient on ventilator, extracorporeal membrane oxygenation, ventricular assist device, or inotropes at transplant; recipient serum bilirubin and creatinine closest to transplant, ratio of donor weight to recipient weight, underlying cardiac diagnosis, crossmatch results, transplant year, and HLA matching at the A, B, and DR loci.

RESULTS

Complete typing at the C locus occurred in 2,429 of 4,731 transplants (51%), and complete typing at the DQ locus occurred in 3,498 of 4,731 transplants (74%). Patient factors were similar in C-match and C-no, except for year of transplant (median year, 2007 [interquartile range, 1997-2010] vs year 2005 [interquartile range, 1996-2009], respectively; p = 0.03) and the degree of HLA matching at the A, B, and DR loci (high level of HLA matching in 11.9% vs 3%, respectively; p < 0.01). Matching at the C locus was not associated with a decreased risk of graft loss (median graft survival: 13.1 years [95% confidence interval {CI}, 11.5-14.8] in C-no vs 15.1 years [95% CI, 13.5-16.6) in C-match, p = 0.44 log-rank; hazard ratio, 0.93; 95% CI, 0.76-1.15; p = 0.52). DQ-match did not differ from DQ-no in any of the analyzed patient factors, except DQ-match was more likely to have high degree of matching at the A, B, and DR loci vs DQ-no (9.8% vs 3.2%, p < 0.01). Matching at the DQ locus was not associated with decreased risk of graft loss (median graft survival: DQ-no, 13.1 years [95% CI, 11.7-14.6) vs DQ-match, 13.0 years [95% CI, 11.4-14.6], p = 0.80, log-rank; hazard ratio, 0.95; 95% CI, 0.81-1.1; p = 0.51.

CONCLUSIONS

Complete typing at the C locus of both donor and recipient occurs less often then typing at the DQ locus. A higher degree of donor-recipient HLA matching at the C locus or the DQ locus appears not to confer any graft survival advantage.

Antibody-mediated rejection of the cardiac allograft: where do we stand in 2012?

PURPOSE OF REVIEW

The review will discuss the current pathological criteria for the diagnosis and classification of antibody-mediated rejection (AMR) in the cardiac allograft.

RECENT FINDINGS

Until recently, the diagnosis of AMR required clinical dysfunction, presence of donor specific antibodies and pathological alterations. The concept of asymptomatic AMR and its adverse long-term outcomes created, in part the need to reevaluate diagnostic criteria. The results of a recent consensus meeting sponsored by International Society For Heart And Lung Transplantation are discussed.

SUMMARY

The diagnosis of AMR rests on histopathological and immunophenotypic findings. These provide the basis for a new grading scheme.

Successful ICU Care of a 14-Year-Old With Total Artificial Circulation Using Two Ventricular Assist Devices for 118 Days

Within the first year following orthotopic heart transplantation, the patient is at risk of graft failure, rejection, and infection. Late mortality is often due to allograph vasculopathy. Most of the patients with primary graft failure will usually recover with temporary mechanical ventricular assist support; however, on occasion the patient must be retransplanted. For the patient who suffers primary graft failure necessitating explanation and bridging until a new suitable graft is found, there are several total artificial heart options. However, in the pediatric population these options are limited. The authors’ surgical colleagues were able to fashion a paracorporeal total artificial heart constructed with 2 ventricular assist devices. In this case report, the authors discuss a pediatric patient who had to be explanted and supported for an extended amount of time. This article describes the incidence of cardiomyopathy in juvenile rheumatoid arthritis patients, the choice of extracorporeal membrane oxygenation/extracorporeal complete life support versus ventricular assist devices for support, the major causes of primary graft failure, and the authors’ experience in caring for an adolescent with such a device for a protracted length of time (118 days).

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.

Morphologic and immunohistochemical findings in antibody-mediated rejection of the cardiac allograft

The recognition and acceptance of the entity of antibody-mediated rejection (AMR) of solid organs has been slow to develop. Greatest acceptance and most information relates to cardiac transplantation. AMR is thought to represent antibody/complement mediated injury to the microvasculature of the graft that can result in allograft dysfunction, allograft loss, accelerated graft vasculopathy, and increased mortality. The morphologic hallmark is microvascular injury with immunoglobulin and complement deposition in capillaries, accumulation of intravascular macrophages, and in more severe cases, microvascular hemorrhage and thrombosis, with inflammation and edema of the affected organ. Understanding of the pathogenesis of AMR, criteria and methods for diagnosis, and treatment strategies are still in evolution, and will be addressed in this review.

Is heart transplantation for complex congenital heart disease a good option? A 25-year single centre experience

OBJECTIVES

Heart transplantation (HTx) in patients with complex congenital heart disease (CHD) is a challenge because of structural anomalies and multiple previous procedures. We analysed our results in adult and paediatric patients to evaluate outcome and assess risk factors affecting mortality.

METHODS

Between 1985 and 2011, among 839 patients who underwent HTx, 85 received transplantation for end-stage CHD. Patients were divided into four age subgroups: <1 year (8 patients, Group I), 1-10 years (20 patients, Group II), 11-18 years (24 patients, Group III) and >18 years (33 patients, Group IV) and into two time periods: 1985-2000 (47 patients) and 2001-2011 (38 patients). Anatomical diagnoses were single-ventricle defect in 37 patients (44%) and two-ventricle defect in 48 patients (56%). Seventy-three patients (86%) had undergone one or more cardiac surgical procedures prior to HTx (mean 2.4 ± 0.9). Twenty-two of them were suffering from Fontan failure. Mean pulmonary artery pressure was 25.2 ± 14.2 mmHg. Mean transpulmonary gradient was 9.4 ± 6.9 mmHg.

RESULTS

Mean follow-up after HTx was 7.8 ± 6.8 years. Survival at 1 month was 37.7% in Group I, 85.8% in Group II, 96.8% in Group II and 98.4% in Group IV and was significantly worse in younger recipients. Overall 30-day mortality was 17.6%. Currently 56 patients (65.8%) are alive. Overall survival at 1, 5, 10 and 15 years is 83-, 73-, 67- and 58%, respectively. There were 14 late deaths. Univariate analysis found that risk factors for early and late death were those related to recipient illness, such as pre-transplant creatinine, intravenous inotropic drugs, intravenous diuretics, mechanical ventilation and presence of protein-losing enteropathy (PLE). Multivariate analysis for all events (early and late deaths) identified preoperative mechanical ventilation as an independent risk factor for mortality. Number of previous procedures did not influence survival. Previous Fontan procedure did not increase mortality. We documented the reversibility of PLE in survivors.

CONCLUSIONS

We demonstrated that heart transplantation for patients with CHD can be performed with the expectation of excellent results. Previous procedures, including the Fontan operation, do not reduce survival. Mortality is related to preoperative patient condition. We advocate early referral of complex CHD patients for transplant assessment and for inclusion in waiting lists before the detrimental effects of end-stage failure manifest themselves.

Biomarkers of heart transplant rejection: the good, the bad, and the ugly!

Acute cellular rejection (ACR), antibody-mediated rejection (AMR), and cardiac allograft vasculopathy (CAV) are important limitations for the long-term survival of heart transplant recipients. Although much progress has been made in reducing ACR with modern immunosuppressive treatments and continuous biopsy surveillance, there is still a long way to go to better understand and treat AMR, to enable early detection of patients at risk of CAV, and to reduce the development and sustained progression of this irreversible disease that permanently compromises graft function. This review considers the advances made in ACR detection and treatment allowing a more prolonged survival and the risk factors leading to endothelial injury, dysfunction, inflammation, and subsequent CAV, as well as new treatment modalities for CAV. The review also evaluates the controversies around the definition, pathogenesis, and treatment of AMR. To date, much progress is still needed to significantly reduce post-transplant complications and increase graft and patient survival.

Multiple risk factors before pediatric cardiac transplantation are associated with increased graft loss

Identification of heart transplant recipients at highest risk for a poor outcome could lead to improved posttransplantation survival. A chart review of primary heart transplantations from 1993 to 2006 was performed. Analysis was performed to evaluate the risk of graft loss for those with a transplantation age less than 1 year, congenital heart disease (CHD), elevated pulmonary vascular resistance (index > 6), positive panel reactive antibody or crossmatch, liver or renal dysfunction, mechanical ventilation, or mechanical circulatory support (MCS). Primary transplantation was performed for 189 patients. Among these patients, 37% had CHD, 23% had mechanical ventilation, and 6% had renal dysfunction. Overall graft survival was 82% at 1 year and 68% at 5 years. The univariate risk factors for graft loss included mechanical ventilation (hazard ratio [HR], 1.9; 95% confidence interval [CI], 1.15-3.18), CHD (HR, 1.68; 95% CI, 1.04-2.70), and renal dysfunction (HR, 3.05; 95% CI, 1.34-6.70). The multivariate predictors of graft loss were CHD (HR, 1.8; 95% CI, 1.02-2.64), mechanical ventilation (HR, 1.9; 95% CI, 1.13-3.10), and the presence of two or more statistically significant univariate risk factors (SRF) (HR, 3.8; 95% CI, 2.00-7.32). Mechanical ventilation, CHD, and the presence of two or more SRFs identify pediatric patients at higher risk for graft loss and should be considered in the management of children with end-stage heart failure.

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.

Humoral Rejection after Pediatric Heart Transplantation: A Case Report

Humoral rejection was observed 2 years after heart transplantation in a 10-year-old African American girl with sickle cell disease. Hemodynamic compromise developed, and the patient started treatment with extracorporeal membrane oxygenation within 24 hours of admission. With cellular rejection initially believed to be the cause, administration of thymoglobulin and high-dose steroids was initiated. Human leukocyte antigen antibody analysis revealed high titers of donor-specific class I and II antibodies. Aggressive treatment for antibody-mediated rejection was started with plasmapheresis and administration of intravenous immune globulin and ritux-imab. The patient displayed clinical signs of infection and was treated with antimicrobial, antiviral, and antifungal agents. Computed tomography of the chest suggested asperigillous infection. The patient underwent a left upper lobectomy. The patient recovered and has done well, now 4 years after having received the heart transplant. Antibody-mediated rejection should be considered early in heart transplant patients presenting with hemodynamic compromise and may respond to aggressive antibody and B cell–directed therapy. Vigilance for secondary infections, especially during treatment for rejection, is crucial.

Mechanisms of complement activation, C4d deposition, and their contribution to the pathogenesis of antibody-mediated rejection

Complement split products have emerged as useful markers of antibody-mediated rejection in solid organ transplants. One split product, C4d, is now widely accepted as a marker for antibody-mediated rejection in renal and cardiac allografts. This review summarizes the rationale for the use of C4d as a marker of antibody-mediated rejection, along with the clinical evidence supporting its use in the clinical diagnosis of antibody-mediated rejection. Antibody-independent mechanisms by which C4d can be activated by the classical and lectin pathways of complement activation are also identified. Finally, mechanisms by which complement activation stimulates effector cells (neutrophils, monocytes, macrophages, platelets, and B and T lymphocytes) as well as target cells (endothelial cells) are discussed in relation to antibody-mediated allograft rejection.

Asymptomatic antibody-mediated rejection after heart transplantation predicts poor outcomes

BACKGROUND

Antibody-mediated rejection (AMR) has been associated with poor outcome after heart transplantation. The diagnosis of AMR usually includes endomyocardial biopsy findings of endothelial cell swelling, intravascular macrophages, C4d+ staining, and associated left ventricular dysfunction. The significance of AMR findings in biopsy specimens of asymptomatic heart transplant patients (normal cardiac function and no symptoms of heart failure) is unclear.

METHODS

Between July 1997 and September 2001, AMR was found in the biopsy specimens of 43 patients. Patients were divided into 2 groups: asymptomatic AMR (AsAMR, n = 21) and treated AMR (TxAMR with associated left ventricular dysfunction, n = 22). For comparison, a control group of 86 contemporaneous patients, without AMR, was matched for age, gender, and time from transplant. Outcomes included 5-year actuarial survival and development of cardiac allograft vasculopathy (CAV). Patients were considered to have AMR if they had > or = 1 endomyocardial biopsy specimen positive for AMR.

RESULTS

The 5-year actuarial survival for the AsAMR (86%), TxAMR (68%), and control groups (79%) was not significantly different (p = 0.41). Five-year freedom from CAV (> or = 30% stenosis in any vessel) was AsAMR, 52%; TxAMR, 68%; and control, 79%. Individually, freedom from CAV was significantly lower in the AsAMR group compared with the control group (p = 0.02). There was no significant difference between AsAMR vs TxAMR and TxAMR vs control for CAV.

CONCLUSIONS

Despite comparable 5-year survival with controls after heart transplantation, AsAMR rejection is associated with a greater risk of CAV. Trials to treat AsAMR to alter outcome are warranted.

Late outcomes of pediatric heart transplantation are independent of pre-transplant diagnosis and prior cardiac surgical intervention

BACKGROUND

An increasing number of children are being referred for cardiac transplantation after (1) failing conventional corrective or palliative surgical reconstruction, (2) after stabilization with mechanical circulatory support devices, and (3) when primary graft failure or advanced cardiac allograft vasculopathy are established.

METHODS

The records of 417 infants and children (age range, 0-18 years) who underwent cardiac transplantation from November 1985 through December 2005 at Loma Linda University Children's Hospital were retrospectively reviewed. The pre-transplantation diagnosis was used to divide patients into 3 groups: primary cardiomyopathy (CM), 103; hypoplastic left heart syndrome (HLHS), 154; and other complex congenital heart disease (CCHD), 160. These groups were compared and analyzed for differences in early and late morbidity and mortality.

RESULTS

Operative mortality was significantly lower in the CM group compared with the HLHS (p < 0.02;) and CCHD groups (p < 0.01). Long-term actuarial recipient survival, however, was similar for all groups. The 15-year actuarial survival was 59% for the CM Group, 57% for the HLHS Group, and 50% for the CCHD Group. Actuarial survival after retransplantation is not statistically different from that with primary cardiac transplantation.

CONCLUSION

Although peri-operative survival was lower in infants and children with HLHS and CCHD compared with those with CM, long-term survival has been the same for all groups. Late survival after retransplantation was not statistically different than among those with primary cardiac transplantation.

Characterization of c4d immunostaining utilizing paraffin-embedded tissue of nonpresensitized pediatric heart transplant patients

Immunoperoxidase techniques for demonstration of complement split product C4d on paraffin-embedded endomyocardial biopsy samples have been used for the evaluation of humoral rejection mainly in adult heart transplantation. Interpretation of suspected humoral rejection in children requires knowledge of the pattern and frequency of C4d deposition in nonpresensitized pediatric heart transplantation patients. Paraffin-embedded endomyocardial biopsy samples of 65 patients with no rejection, acute cellular rejection (ACR), or early ischemic/reperfusion injury were studied. Six biopsies within each grade of ACR both early (<6 months) and late (>6 months) after heart transplantation were reviewed, as were 5 biopsies of ischemic/reperfusion injury. None of the subjects was sensitized prior to transplant. All slides were blindly evaluated for histologic features traditionally associated with humoral rejection. C4d staining was quantified by counting the number of positive capillaries in 10 random high-power fields (hpf). C4d positivity (C4d+) was defined as >10 capillaries/10 hpf. C4d+ was observed in 6 (9%) endomyocardial biopsy samples; 2 in the early and 4 in the late ACR groups. Four had ACR grades 1A/B, and 2 had grade 3B/4. Thirteen (20%) endomyocardial biopsy samples had histologic features suggestive of humoral rejection. Of these, only 2 were C4d+ and both had ACR grade 3B/4. No C4d+ staining was found in the ischemic/reperfusion injury group. C4d immunostaining was negative in endomyocardial biopsy samples of the majority of our patients (91%). Endomyocardial biopsy samples with C4d+ did not show consistent ACR grade or time specificity. Contrary to previously reported data, none of the ischemic/reperfusion injury endomyocardial biopsy samples was C4d+, and histologic features alone were poor predictors of C4d+.

The use of Doppler tissue imaging to predict cellular and antibody-mediated rejection in pediatric heart transplant recipients

DTI indices have been associated with cellular rejection in adult heart transplant recipients, but their predictive value in pediatric recipients is unknown. The purpose of this study was to evaluate DTI measures in the detection of cellular and AMR in pediatric heart transplant recipients. One hundred and forty-eight pediatric heart transplant recipients who had 267 cardiac catheterization procedures with EMB, echocardiogram with DTI, and BNP level performed on the same day were included in the study. For the mitral and tricuspid valves, the ratios (E/E') between the early diastolic inflow velocity by pulsed Doppler (E, m/s) and the early diastolic annular velocity by DTI (E', m/s) were obtained and compared between subjects with and without rejection. Of the 148 recipients, 30 subjects had a total of 37 episodes of rejection: 10 cellular (>or=1B), 17 AMR, and 10 biopsy-negative clinical rejection. Mitral and tricuspid valve E/E' ratios were significantly higher in rejectors than in non-rejectors (5.5 +/- 1.3 vs. 4.4 +/- 1.4, p < 0.001 and 4.9 +/- 2.1 vs. 4.1 +/- 1.5, p < 0.01, respectively). By multivariate linear regression, mitral valve E/E' was an independent predictor of rejection. Mitral and tricuspid valve E/E' <5.0 had 93% and 89% NPV, respectively, for rejection. Mitral and tricuspid valve E/E' ratios <5.0 may be useful non-invasive screening measures to exclude rejection in pediatric heart transplant recipients.

Treatment with riboflavin and ultraviolet light prevents alloimmunization to platelet transfusions and cardiac transplants

BACKGROUND

Functional leukocytes in blood transfusions can cause alloimmunization. Previous studies have shown that exposure of platelet concentrates to riboflavin and light (Mirasol PRT treatment) causes irreparable modification of nucleic acids. This treatment does not interfere with platelet function but does inhibit a wide range of immunological functions of leukocytes present in platelet concentrates. The current study evaluated the ability of Mirasol treatment to prevent alloimmunization by platelet transfusions in rats.

METHODS

Lewis rats received eight transfusions of untreated or Mirasol-treated platelets containing leukocytes from DA rats. Animals were subsequently challenged with a heart transplant under cyclosporine treatment.

RESULTS

Mirasol treatment caused apoptosis of the leukocytes as measured by annexin V and CD45 staining. Complement split products were deposited on the apoptotic bodies in the platelet pack. The primary and secondary immunoglobulin (Ig) M and IgG responses in rats that received Mirasol-treated platelets were almost completely abolished compared to animals that received untreated platelets. Untreated platelet transfusions elicited strong IgG responses that were associated with rapid rejection of subsequent heart transplants. Rejected hearts contained macrophage infiltrates and C4d deposits. In contrast, no grafts were rejected by recipients transfused with Mirasol-treated platelets. Macrophage infiltrates and C4d deposits were decreased in these grafts. Recipients that were presensitized to untreated platelets were capable of producing a memory response to Mirasol-treated platelets that caused accelerated rejection of subsequent transplants.

CONCLUSIONS

Transfusions of platelets that were treated with riboflavin and ultraviolet light prevented presensitization to transplants. However, Mirasol-treated platelets were immunogenic in presensitized recipients.

Cardiac transplant outcomes in pediatric patients with pre-formed anti-human leukocyte antigen antibodies and/or positive retrospective crossmatch

BACKGROUND

Children undergoing heart transplantation who have preformed anti-human leucocyte antigen (HLA) panel reactive antibodies (PRA) or positive retrospective crossmatch (XM) may be at increased risk for rejection and graft failure. We assessed outcomes of transplant recipients with either positive PRA before transplant or positive retrospective XM.

METHODS

A review of 148 heart transplant patients between 1990 and 2006 was undertaken, identifying transplants in patients with pre-transplant PRA > 1% and/or a positive XM. Demographic information and detailed post-transplant outcomes including episodes of rejection, infection, and graft failure were recorded.

RESULTS

There were 11 PRA positive (PRA+) transplants, 135 PRA negative (PRA-) transplants, and no PRA data on 2. There were 14 XM+ transplants, 115 XM- transplants, and no XM data on 19. Kaplan-Meier graft survival was better in XM- than XM+ patients (p < 0.015), but not different between PRA+ and PRA- Groups. Timing of first rejection and number of rejection episodes were not different between XM+ and XM- Groups or between PRA+ and PRA- Groups. Infections were not different between PRA or XM Groups. Four patients were PRA+/XM- (all PRA, 1%-10%), 7 were PRA-/XM+, and 7 were PRA+/XM+ (6 of 7 PRA >10%).

CONCLUSIONS

Pediatric heart transplant patients whose retrospective XM is positive are at significantly increased risk for graft failure. Elevated pre-transplant PRA may not predict increased risk of graft failure, although markedly positive PRA (>10%) predicts a positive retrospective XM. Improved treatment for pediatric transplant patients with a positive retrospective XM is needed.

Acute antibody-mediated rejection following heart transplantation

Acute antibody-mediated rejection (AMR) in heart transplantation is often associated with hemodynamic compromise, and is associated with increased mortality and development of accelerated transplant coronary artery disease (TCAD). The diagnosis of AMR has historically been controversial and outcomes with aggressive immunosuppressive therapy including plasmapheresis and cyclophosphamide are poor. Advances in diagnostic techniques like the demonstration of immunopathologic evidence for antibody-mediated rejection by deposition of the complement split product C4d in tissue and detection of anti-HLA antibodies by flow cytometry will assist in further characterizing AMR. Immunosuppression targeting B-lymphocytes and use of m-TOR inhibitors to alter the predilection to develop TCAD and improve survival in AMR remains to be proven.