Risk stratification to determine the impact of induction therapy on survival, rejection and adverse events after pediatric heart transplant: A multi-institutional study

Assessing Donor-Recipient Size Mismatch in Pediatric Heart Transplantation: Lessons Learned From Over 7,500 Transplants

BACKGROUND

To date, no studies have identified an optimal metric to match donor-recipient (D-R) pairs in pediatric heart transplantation (HT).

OBJECTIVES

This study sought to identify size mismatch metrics that predicted graft survival post-HT.

METHODS

D-R pairs undergoing HT in Pediatric Heart Transplant Society database from 1993 to 2021 were included. Effects of size mismatch by height, weight, body mass index, body surface area, predicted heart mass, and total cardiac volume (TCV) on 1- and 5-year graft survival and morbidity outcomes (rejection and cardiac allograft vasculopathy) were evaluated. Cox models with stepwise selection identified size metrics that independently predicted graft survival.

RESULTS

Of 7,715 D-R pairs, 36.0% were well matched (D-R ratio: -20% to +20%) by weight, 39.0% by predicted heart mass, 50.0% by body surface area, 57.0% by body mass index, 71.0% by height, and 93.0% by TCV. Of all size metrics, only D-R mismatch by height and TCV predicted graft survival at 1 and 5 years. Effects of D-R size mismatch on graft survival were nonlinear. At both 1 and 5 years post-HT, D-R undersizing and oversizing by height led to increased graft loss, with graft loss observed more frequently with undersizing. Moderately undersized donors by height (D-R ratio: <-30%) frequently experienced rejection post-HT (P < 0.001). Assessing D-R size matching by TCV, minimal donor undersizing was protective, while oversizing up to 25% was not associated with increased graft loss.

CONCLUSIONS

In pediatric HT, D-R appear most optimally matched using TCV. Only D-R size mismatch by TCV and height independently predicts graft survival. Standardizing size matching across centers may reduce donor discard.

Increased risk of infections in pediatric Fontan patients after heart transplantation

BACKGROUND

Infectious complications are a major cause of morbidity and mortality after HT. Fontan patients may be more susceptible to post-HT infections.

METHODS

This was a single-center, retrospective cohort analysis of pediatric patients undergoing HT for FF physiology or DCM, who underwent induction with ATG. The primary endpoint was an infection in the first 180 days post-HT, defined as positive (1) blood/urine/respiratory culture; (2) viral PCR; (3) skin or wound infection; and/or (4) culture-negative infection if ≥5 days of antibiotics were completed. Secondary endpoints included (1) cell counts after ATG; (2) PTLD; and (3) rejection (≥Grade 2R ACR or pAMR2) in the first 180 days post-HT.

RESULTS

A total of 59 patients (26 FF, 33 DCM) underwent HT at 14.7 (IQR 10.6, 19.5) and 11.7 (IQR 1.4, 13.6) years of age, respectively. The median total ATG received was 7.4 (IQR 4.9, 7.7) vs 7.5 (IQR 7.3, 7.6) mg/kg (p = NS) for FF and DCM patients, respectively. Twenty-three patients (39%) developed an infection 180 days post-HT, with a higher rate of infection in FF patients (54% vs 27%, p = .03). Adjusted for pre-transplant absolute lymphocyte count, FF patients had a higher risk of infection at 30 days post-HT (OR 7.62, 95% CI 1.13-51.48, p = .04). There was no difference in the incidence of PTLD (12% vs 0%; p = .08) or rejection (12% vs 21%; p = .49).

CONCLUSION

Compared to DCM patients, FF patients have a higher risk of infection. Modifications to induction therapy for FF patients should be considered.

Impact of induction therapy on cytomegalovirus infection and post-transplant outcomes in pediatric heart transplant recipients receiving routine antiviral prophylaxis

OBJECTIVES

Induction therapy has been increasingly used in pediatric heart transplantation. This study evaluated the impact of anti-thymocyte globulin (ATG) versus basiliximab as induction therapy on post-transplant cytomegalovirus (CMV) infection, rejection at 1 year, coronary allograft vasculopathy (CAV), and mortality in pediatric heart transplant recipients receiving antiviral prophylaxis.

RESULTS

Of the 96 patients (age < 18 years) analyzed, 46 (47.9%) patients received basiliximab, and 50 (52.1%) received ATG. Median follow-up was 3.0 (IQR, 1.7-4.9) years with 32.3% reporting CMV infection. The ATG group, as compared with the basiliximab group, had similar incidences of CMV infection (36% vs. 28.3%, p = .418), CMV viremia (22% vs. 19.6%, p = .769), and CMV-positive tissue biopsy (30% vs. 22%, p = .486). The ATG group had lower incidences of rejection at 1 year (16% vs. 36.9%, p = .022) and CAV (4% vs. 23.9%, p = .006) with no difference in mortality (8% vs. 15.2%, p = .343), compared with the basiliximab group. Multivariate analysis showed that induction with ATG was associated with a lower risk of rejection at 1 year (OR, .31; 95% CI, .09-.94; p = .039) with no impact on the incidences of CMV infection (HR, 2.06; 95% CI, .54-7.89; p = .292), CAV (HR, .30; 95% CI, .04-2.58; p = .275), and mortality (HR, .39; 95% CI, .09-1.82; p = .233) compared to basiliximab induction.

DISCUSSION AND CONCLUSIONS

In conclusion, induction with ATG was associated with reduction in risk of rejection at 1 year with no effects on CMV infection, CAV, and mortality in pediatric heart transplant recipients with universal antiviral prophylaxis compared with basiliximab induction therapy.

Practice variation in the diagnosis of acute rejection among pediatric heart transplant centers: An analysis of the pediatric heart transplant society (PHTS) registry

BACKGROUND

Freedom from rejection in pediatric heart transplant recipients is highly variable across centers. This study aimed to assess the center variation in methods used to diagnose rejection in the first-year post-transplant and determine the impact of this variation on patient outcomes.

METHODS

The PHTS registry was queried for all rejection episodes in the first-year post-transplant (2010-2019). The primary method for rejection diagnosis was determined for each event as surveillance biopsy, echo diagnosis, or clinical. The percentage of first-year rejection events diagnosed by surveillance biopsy was used to approximate the surveillance strategy across centers. Methods of rejection diagnosis were described and patient outcomes were assessed based on surveillance biopsy utilization among centers.

RESULTS

A total of 3985 patients from 56 centers were included. Of this group, 873 (22%) developed rejection within the first-year post-transplant. Surveillance biopsy was the most common method of rejection diagnosis (71.7%), but practices were highly variable across centers. The majority (73.6%) of first rejection events occurred within 3-months of transplantation. Diagnosis modality in the first-year was not independently associated with freedom from rejection, freedom from rejection with hemodynamic compromise, or overall graft survival.

CONCLUSIONS

Rejection in the first-year after pediatric heart transplant occurs in 22% of patients and most commonly in the first 3 months post-transplant. Significant variation exists across centers in the methods used to diagnose rejection in pediatric heart transplant recipients, however, these variable strategies are not independently associated with freedom from rejection, rejection with hemodynamic compromise, or overall graft survival.

EBV Predicts Post-Pediatric Heart Transplant Malignancy; Induction Therapy and Tacrolimus Don't

BACKGROUND

Patients after heart transplantation are at increased risk for malignancy secondary to immunosuppression and oncogenic viral infections. Most common amongst children is post-transplant lymphoproliferative disorder (PTLD), occurring in 5-10% of patients. We utilized a national database to examine incidence and risk factors for post-transplant malignancy.

METHODS

The United Network for Organ Sharing (UNOS) database was queried for pediatric (<18 years) heart transplant recipients from 10/1987-10/2019. Kaplan-Meier analysis was performed to assess freedom from malignancy post-transplant. Cox regression was performed to generate hazard ratios (HR [95% CI]) for risk of malignancy development.

RESULTS

Of 8,581 pediatric heart transplant recipients, 8.1% developed malignancy over median follow-up time of 6.3 years, with PTLD compromising the majority (86.4%) of diagnosed cancers. The incidence of PTLD development was 1.3% and 4.5% at one and five years. Older age at the time of transplant was protective against the development of malignancy (HR 0.98 [0.96-0.99], p<0.001), whereas a history of previous malignancy (HR 1.9 [1.2-3.0], p=0.007) and Ebstein-Barr virus (EBV) recipient-donor mismatch (HR 1.7 [1.3-2.2], p<0.001) increased the risk. Use of induction therapy (utilized in 78.9% of the cohort) did not increase malignancy risk (p=0.355); nor did use of maintenance tacrolimus (p=0.912).

CONCLUSIONS

PTLD occurred after 7% of pediatric heart transplants, with risk increased by younger age and EBV mismatch, highlighting the importance of PTLD monitoring in EBV seronegative recipients. Induction therapy, utilized in the majority of pediatric heart transplants, does not seem to increase post-transplant malignancy, nor does the most commonly used calcineurin inhibitor tacrolimus.

Hospitalizations for Respiratory Syncytial Virus and Vaccine Preventable Infections following Pediatric Heart Transplantation

OBJECTIVE

To determine the risk factors for acquiring a respiratory syncytial virus (RSV) and vaccine-preventable infections (R/VPI) in pediatric heart transplant recipients and the associated morbidity and hospital resource use.

STUDY DESIGN

Patients <18 years who underwent heart transplantation from September 2003 to December 2018 at hospitals using the Pediatric Health Information System database were identified. Their transplant hospitalization and subsequent hospitalizations for R/VPI through December 2018 were analyzed. Risk factors for R/VPI hospitalizations were evaluated using negative regression binomial models adjusted for demographic and clinical confounders. Total hospital costs were adjusted for 2018 US$.

RESULTS

Of 3815 transplant recipients, 681 (17.9%) had an R/VPI hospitalization during 23 746 available person-years of follow-up. There were 984 R/VPIs diagnosed during 951 hospitalizations, and 440 (44.7%) occurred the first year after transplantation. The most common causes were RSV (n = 380; 38.6%), influenza (n = 265; 26.9%), and pneumococcus (n = 105; 10.7%). In adjusted analyses, there was an increased risk of R/VPI hospitalization in patients requiring mechanical circulatory support before transplantation, patients receiving induction with ≥2 immunosuppressive agents, and patients <2 years in the first year after transplantation. The median length of stay for an R/VPI hospitalization was 4 days (IQR, 2-8 days) with a median total cost of $11 081 (IQR, $6215-$24 322).

CONCLUSIONS

Hospitalization for R/VPIs occurred frequently after heart transplantation and were associated with significant costs. Potential strategies to minimize R/VPI include expanding vaccine use through accelerated immunization schedules, further studies of use of palivizumab beyond 2 years of age, and immunogenicity monitoring after vaccination with re-immunization based on guidelines.

Use of induction therapy in pediatric heart transplant recipients in Switzerland - Analysis of the Swiss national database

BACKGROUND

Data on individualized immunosuppressive protocols for the pediatric heart recipients are missing in Europe. To contribute to this very small but specialized field, we describe the use of induction therapy (IT) in pediatric heart transplant patients in Switzerland and the retrospective outcomes.

METHOD

This is a retrospective national database analysis of children <19 years of age at time of heart transplantation (HT) from 05/2008-01/2018. Use of IT or no IT, use of steroids, calculated panel reactive antibodies (cPRA) and outcomes (Mortality, post-transplant lymphoproliferative disease (PTLD), rejection rates) were studied within a mean follow-up period of 2.9 years (0.2-8.1 years).

RESULTS

All 32 patients (12♂, 20♀), median age at HT of 6.4 years (24 days - 18 years) received IT using either polyclonal antibodies (ATG; 72%) or interleukin-2 receptor antagonist (anti-IL-2R mAb; 28%). Length of treatment was median of 4 (1-63) days. At time of HT all patients received steroids, while at discharge 32% and one year after HT 19%. Kaplan-Meier analysis of survival revealed a one-year survival of 86%. Three out of 7 patients with elevated cPRA (43%) died. Median time to first treated rejection was 19.4 months (±60.5 SD) without significant difference if treated with anti-IL-2R mAb or ATG (p:0.5). No development of PTLD, chronic renal failure needing ongoing renal replacement therapy or diabetes mellitus were recorded.

DISCUSSION

This is the first report of the national practice use of IT within Switzerland. It reveals a high use of IT, no development of PTLD and a low use of steroids at one-year post HT.

Impact of induction strategy change on first-year rejection in pediatric heart transplantation at a single center-From postoperative basiliximab to either postoperative anti-thymocyte globulin or preoperative basiliximab

BACKGROUND

Our pediatric heart transplant center transitioned from post-bypass basiliximab (BAS) induction to either anti-thymocyte globulin (ATG) or pre-bypass BAS. The purpose of this study was to compare first-year rejection rates before and after this change.

METHODS

A single-center retrospective analysis was conducted of pediatric heart transplant recipients from 2010 to 2019. Primary outcome was first-year rejection. Bivariate analysis, Kaplan-Meier curves, and multivariable regression were performed across eras.

RESULTS

Forty-three early era patients (55%) received post-bypass BAS, and 35 late era patients (45%) received pre-bypass BAS (n = 17) or ATG (n = 18). First-year rejection decreased in the late era (31% vs 53%, p = .05). This finding was more pronounced after excluding infants (38% vs 73%, p = .006). Late era was associated with a decreased likelihood of rejection (all cohort OR 0.19, 95% CI 0.05-0.66; infants excluded OR 0.17, 95% CI 0.04-0.61). No differences in post-transplant lymphoproliferative disease, donor-specific antibody, or infection were observed.

CONCLUSIONS

Fewer late era patients receiving ATG or pre-bypass BAS induction had first-year rejection compared to the early era patients receiving standard post-bypass BAS induction. This programmatic shift in induction strategy was readily achievable and potentially effective in reducing first-year rejection.

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.

Basiliximab impairs regulatory T cell (TREG) function and could affect the short-term graft acceptance in children with heart transplantation

CD25, the alpha chain of the IL-2 receptor, is expressed on activated effector T cells that mediate immune graft damage. Induction immunosuppression is commonly used in solid organ transplantation and can include antibodies blocking CD25. However, regulatory T cells (Tregs) also rely on CD25 for their proliferation, survival, and regulatory function. Therefore, CD25-blockade may compromise Treg protective role against rejection. We analysed in vitro the effect of basiliximab (BXM) on the viability, phenotype, proliferation and cytokine production of Treg cells. We also evaluated in vivo the effect of BXM on Treg in thymectomized heart transplant children receiving BXM in comparison to patients not receiving induction therapy. Our results show that BXM reduces Treg counts and function in vitro by affecting their proliferation, Foxp3 expression, and IL-10 secretion capacity. In pediatric heart-transplant patients, we observed decreased Treg counts and a diminished Treg/Teff ratio in BXM-treated patients up to 6-month after treatment, recovering baseline values at the end of the 12-month follow up period. These results reveal that the use of BXM could produce detrimental effects on Tregs, and support the evidence suggesting that BXM induction could impair the protective role of Tregs in the period of highest incidence of acute graft rejection.

Comparison of basiliximab vs antithymocyte globulin for induction in pediatric heart transplant recipients: An analysis of the International Society for Heart and Lung Transplantation database

This study aims to compare 2 common induction strategies, basiliximab and ATG. Analysis of the ISHLT transplant registry was performed. The database was queried for pediatric heart transplants from January 1, 2000, to June 30, 2015, who had received induction with basiliximab or ATG. Primary end-point was graft survival. Secondary end-points included 1-year survival and 1-year conditional survival. There were 3158 heart transplants who received induction with basiliximab or ATG. The ATG cohort was younger, more likely to have congenital heart disease or be a retransplant, have a higher PRA, longer ischemic time, and been transplanted earlier in the study period (all P<.01). There was no difference in graft loss in the basiliximab cohort compared to the ATG cohort (HR 1.18 P=.06). On conditional 1-year survival analysis, basiliximab induction was associated with graft loss (HR=1.35 95% CI 1.1-1.7, P<.01), and in the propensity-matched cohort, the basiliximab cohort was more likely to experience rejection prior to discharge (P=.04). Infection prior to discharge was more common in the antithymocyte cohort. Induction with ATG is associated with improved late graft survival compared to basiliximab.

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.

Current state of pediatric cardiac transplantation

Pediatric heart transplantation is standard of care for children with end-stage heart failure. The diverse age range, diagnoses, and practice variations continue to challenge the development of evidence-based practices and new technologies. Outcomes in the most recent era are excellent, especially with the more widespread use of ventricular assist devices (VADs). Waitlist mortality remains high and knowledge of risk factors for death while waiting and following transplantation contributes to decision-making around transplant candidacy and timing of listing. The biggest gap impacting both waitlist and overall survival remains mechanical support options for infants and patients with single ventricle physiology. Though acute rejection has decreased progressively, both diagnosis and management of antibody-mediated rejection has become increasingly challenging and complex, as has the ability to understand the implication of anti-HLA antibodies detected both pre- and post-transplantation-including when and how to intervene. Trends in immunosuppression protocols include more use of induction therapy and steroid avoidance or withdrawal protocols. Common long-term morbidities include renal insufficiency, which can be mitigated with surveillance and renal-sparing strategies, and infections. Functional outcomes are excellent, but significant psychosocial challenges exist in relation to neurodevelopment, non-adherence, and transition from child-centered to adult-centered care. Cardiac allograft vasculopathy (CAV) remains a barrier to long-term survival, though it is more apparent that objective evidence of an impact on the allograft is important with regards to impact on outcomes. Retransplantation is rare in pediatric heart transplant recipients. Pediatric heart transplantation continues to evolve in order to address the challenges of the diverse group of patients that reach end-stage heart failure during childhood.