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

Heart transplantation and biomarkers: a review about their usefulness in clinical practice

Advanced heart failure (AdvHF) can only be treated definitively by heart transplantation (HTx), yet problems such right ventricle dysfunction (RVD), rejection, cardiac allograft vasculopathy (CAV), and primary graft dysfunction (PGD) are linked to a poor prognosis. As a result, numerous biomarkers have been investigated in an effort to identify and prevent certain diseases sooner. We looked at both established biomarkers, such as NT-proBNP, hs-troponins, and pro-inflammatory cytokines, and newer ones, such as extracellular vesicles (EVs), donor specific antibodies (DSA), gene expression profile (GEP), donor-derived cell free DNA (dd-cfDNA), microRNA (miRNA), and soluble suppression of tumorigenicity 2 (sST2). These biomarkers are typically linked to complications from HTX. We also highlight the relationships between each biomarker and one or more problems, as well as their applicability in routine clinical practice.

Chronic intermittent intravenous immunoglobulin in heart transplant recipients with elevated donor-specific antibody levels

Donor-specific antibodies (DSA) are associated with antibody-mediated rejection (AMR) and poor patient survival. In heart transplant, the efficacy of intermittent intravenous immunoglobulin (IVIg) in reducing de novo DSA levels and treating AMR has not been characterized. We retrospectively studied a cohort of 19 patients receiving intermittent IVIg for elevated DSA and examined changes in DSA levels and graft function. Intermittent IVIg infusions were generally safe and well tolerated. Overall, 23 of 62 total DSA (37%) were undetectable after treatment, 21 DSA (34%) had MFI decrease by more than 25%, and 18 (29%) had MFI decrease by less than 25% or increase. The average change in MFI was -51% ± 71% (P < .001). Despite reductions in DSA, among the six patients (32%) with biopsy-confirmed AMR, left ventricular ejection fraction (LVEF) decreased in five (83%) and cardiac index (CI) decreased in three (50%). Conversely, LVEF increased in 91% and CI increased in 70% of biopsy-negative patients. All six AMR patients were readmitted during treatment, four for confirmed or suspected rejection. IVIg infusions may stabilize the allograft in patients with elevated DSA and negative biopsies, but once AMR has developed does not appear to improve allograft function despite decreasing DSA levels.

The clinical impact of donor-specific antibodies on antibody-mediated rejection and long-term prognosis after heart transplantation

PURPOSE OF REVIEW

Outcomes after cardiac transplantation have improved over past decades, but long-term graft survival remains limited in part because of uncertainty regarding clinical implications of donor-specific antibodies (DSAs). The purpose of this review is to consolidate recent advances in knowledge on the topic of DSA and their potential to impact long-term prognosis after heart transplantation.

RECENT FINDINGS

The presence of persistent DSA increases the risk of poor outcome after heart transplantation, including development of antibody-mediated rejection (AMR), graft failure, cardiac allograft vasculopathy, and mortality. Importantly, different DSA vary in clinical significance. DSA capable of activating the complement cascade portend a higher risk of developing AMR. human leukocyte antigen class I and class II antigens are expressed differently within the heart, and so, clinical manifestations of class I and class II DSA vary accordingly. Further, compared with class I, class II DSA carry an increased risk of graft loss and mortality. When comparing preexisting DSA with formation of de-novo DSA, de-novo DSA are associated with worse outcome.

SUMMARY

DSAs are generally associated worse long-term prognosis after heart transplantation but vary in their clinical significance. Recognition of specific risk profiles is essential for guiding posttransplant antibody management.

Understanding the Correlation Between DSA, Complement Activation, and Antibody-Mediated Rejection in Heart Transplant Recipients

BACKGROUND

Donor-specific HLA antibodies (DSA) are associated with increased rates of rejection and of graft failure in cardiac transplantation. The goal of this study was to determine the association of preformed and posttransplant development of newly detected DSA (ndDSA) with antibody-mediated rejection (AMR) and characterize the clinical relevance of complement-activating DSA in heart allograft recipients.

METHODS

The study included 128 adult and 48 pediatric heart transplant patients transplanted between 2010 and 2013. Routine posttransplant HLA antibody testing was performed by IgG single-antigen bead test. The C3d single-antigen bead assay was used to identify complement-activating antibodies. Rejection was diagnosed using International Society for Heart and Lung Transplantation criteria.

RESULTS

In this study, 22 patients were transplanted with preexisting DSA, and 43 patients developed ndDSA posttransplant. Pretransplant (P < 0.05) and posttransplant (P < 0.001) ndDSA were associated with higher incidence of AMR. Patients with C3d + DSA had significantly higher incidence of AMR compared with patients with no DSA (P < 0.001) or patients with C3d-DSA (P = 0.02). Nine (36%) of 25 patients with AMR developed transplant coronary artery disease compared with 17 (15.9%) of 107 patients without AMR (P < 0.05). Among the 47 patients who received ventricular assistant device (VAD), 7 of 9 VAD+ patients with preformed DSA experienced AMR compared with 7 of 38 VAD+ patients without preformed DSA, indicating presensitization to donor HLA significantly increased the risk of AMR (P < 0.01).

CONCLUSIONS

Preformed and posttransplant ndDSA were associated with AMR. C3d + DSA correlates with complement deposition on the graft and higher risk of AMR which may permit the application of personalized immunotherapy targeting the complement pathway.

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.

The clinical impact of donor-specific antibodies in heart transplantation

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

Significance of Anti-HLA Antibodies on Adult and Pediatric Heart Allograft Outcomes

As methods for human leukocyte antigens (HLA) antibody detection have evolved and newer solid phase assays are much more sensitive, the last 15 years has seen a renewed focus on the importance of HLA antibodies in solid organ transplant rejection. However, there is still much controversy regarding the clinical significance of antibody level as depicted by the mean fluorescence intensity of a patient’s neat serum. Emerging techniques, including those that identify antibody level and function, show promise for the detection of individuals at risk of allograft rejection, determination of the effectiveness of desensitization prior to transplant, and for monitoring treatment of rejection. Here, we review current publications regarding the relevance of donor-specific HLA antibodies (DSA) in adult and pediatric heart transplantation (HT) with graft survival, development of antibody-mediated rejection and cardiac allograft vasculopathy (CAV). The negative impact of DSA on patient and allograft survival is evident in adult and pediatric HT recipients. Many questions remain regarding the most appropriate frequency of assessment of pre- and posttransplant DSA as well as the phenotype of DSA memory vs. true de novo antibody using large multicenter adult and pediatric cohorts and state-of-the-art methodologies for DSA detection and characterization.

Donor-specific HLA Antibodies Are Associated With Late Allograft Dysfunction After Pediatric Liver Transplantation

BACKGROUND

The role of donor-specific HLA antibodies (DSA) after pediatric liver transplantation (LTx) is not clearly established. We completed a cross-sectional study to characterize DSA in long-term survivors of pediatric LTx and assess the impact of C1q-binding DSA on allograft outcomes.

METHODS

Serum samples were collected at routine clinic visits from 50 pediatric LTx recipients classified into 3 clinical phenotypes: nontolerant (n = 18) with de novo autoimmune hepatitis (DAIH) and/or late acute cellular rejection (ACR); stable (n = 25) on maintenance tacrolimus; operationally tolerant (n = 7). Samples were blinded, and antibody detection was performed using Luminex single antigen class I and II beads. Patients with positive DSA were tested for C1q-binding DSA.

RESULTS

DSA were detected in 54% (n = 27) of the patients, with the majority directed at HLA class II antigens (DR, 41%; DQ, 53%). Patients with DSA were younger at the time of LTx (P = 0.016) and time of study (P = 0.024). Mean aspartate aminotransferase, alanine aminotransferase, total bilirubin, and gamma glutamyl transferase were higher in DSA-positive patients, though did not reach statistical significance. Nontolerant patients were significantly more likely to have DQ DSA (61%) compared to stable (20%) and tolerant (29%) patients (P = 0.021). The nontolerant phenotype was associated with DSA and C1q-binding DSA, with odds ratios of 13 (P = 0.015) and 8.6 (P = 0.006), respectively. The presence of DQ DSA was associated with DAIH and late ACR, with odds ratios of 12.5 (P = 0.004) and 10.8 (P = 0.006), respectively.

CONCLUSIONS

Allograft dysfunction is not always evident in patients with DSA, but DQ DSA are strongly associated with DAIH, late ACR, and chronic rejection.

Acute Cellular Rejection and C4d Positivity in Heart Transplantation : A Manifestation of Asymptomatic Antibody-Mediated Rejection?

OBJECTIVES

The role of routine C4d staining in endomyocardial biopsy specimens is uncertain. The implications of a diagnosis of acute cellular rejection (ACR) with a positive C4d with or without any evidence of antibody-mediated rejection (AMR) are unclear. This study sought to evaluate a distinct phenotype of ACR+/C4d+ in AMR- patients.

METHODS

Data on C4d, ACR, and AMR were collected. Donor-specific antibody (DSA), panel-reactive antibody (PRA), flow crossmatch, and data on ACR and AMR episodes were also reviewed.

RESULTS

Thirty-five patients were followed. Group I with C4d+ biopsy specimens was compared with group II with C4d- biopsy specimens. ACR greater than 1R was higher in group I compared with group II (50% vs 7.4%; P = .01). Clinical suspicion of AMR, positive retrospective crossmatches, and detection of de novo DSA were also higher in group I.

CONCLUSIONS

Our result indicate that C4d and ACR positivity in posttransplant patients may be a harbinger of a subclinical form of asymptomatic AMR.

The use of circulating donor specific antibody to predict biopsy diagnosis of antibody-mediated rejection and to provide prognostic value after heart transplantation in children

BACKGROUND

Antibody-mediated rejection (AMR) is a significant cause of mortality after heart transplantation (HT). Although the presence of donor specific antibody (DSA) is a risk factor for developing AMR, serial DSA testing is not widely performed. We aimed to investigate the predictive values and prognostic implications of circulating DSA using endomyocardial biopsy as the gold standard for AMR diagnosis in pediatric recipients of HT.

METHODS

We performed a retrospective study in pediatric recipients of HT followed during the period 2009-2013 with at least 1 biopsy paired with DSA testing. Positive DSA was defined at mean fluorescent intensity (MFI) ≥2,000 using single antigen bead testing. Statistical analyses included 2 × 2 contingency tables, receiver operating characteristic analysis for optimal MFI cutoffs, Spearman correlation of MFI strength to AMR grade, and Kaplan-Meier analysis of event-free survival.

RESULTS

Of 66 children included, 27 (41%) had ≥1 DSA positive test. DSA testing had a sensitivity of 92.6%, specificity of 62.2%, positive predictive value of 24.0%, and negative predictive value of 98.5% for biopsy diagnosis of AMR at our institution. There was a statistically significant correlation between higher MFI and higher AMR grade. Patients with positive DSA and AMR had similar survival early after DSA detection but trended toward lower cardiovascular event-free survival later compared with patients without DSA and a negative biopsy.

CONCLUSIONS

The results of DSA testing in this cohort showed excellent sensitivity and negative predictive value for biopsy-diagnosed AMR, suggesting that DSA testing may aid in the non-invasive prediction of AMR absence in HT. The correlation of DSA MFI strength with higher AMR biopsy grade and the trend toward differences in longer term cardiovascular outcomes provide evidence for routine DSA monitoring after pediatric HT.

HLA molecular epitope mismatching and long-term graft loss in pediatric heart transplant recipients

BACKGROUND

Although evidence links HLA allele mismatching to worse outcomes in pediatric heart transplantation, no studies to our knowledge have applied the quantification of structural HLA differences between donor and recipient to risk evaluation. We examine the association between molecular-level HLA mismatching and long-term graft loss in pediatric recipients of heart transplants.

METHODS

HLA Matchmaker was used to quantify the number of mismatched class-specific HLA eplets among 4,851 heart transplant recipients ≤18 years of age in the Scientific Registry of Transplant Recipients (1987-2012). Survival analysis was used to compare long-term probabilities of graft loss by number of eplet mismatches and allele mismatches stratified by eplet mismatches.

RESULTS

Recipients with 10 to 20 or >20 class I (HLA-A and HLA-B) eplet mismatches experienced increased long-term graft loss compared with recipients with <10 class I eplet mismatches (adjusted hazard ratio = 1.23 [95% confidence interval = 1.06-1.42], adjusted hazard ratio = 1.27 [95% confidence interval = 1.08-1.50], respectively). Recipients with 2 to 4 class I allele mismatches had increased long-term graft loss compared with recipients with 0 to 1 class I allele mismatches. Neither class II (HLA-DR) eplet mismatching nor class II allele mismatching was associated with graft loss. On stratification by allele and structural eplet mismatching, only recipients with 2 to 4 class I allele mismatches and ≥10 class I eplet mismatches had an increased probability of graft loss compared with recipients with 0 to 1 class I allele mismatches (adjusted hazard ratio = 1.42 [95% confidence interval = 1.09-1.57]).

CONCLUSIONS

Molecular-level HLA mismatching may aid in identifying recipients at increased risk of long-term graft loss who could benefit from intensified post-transplant surveillance and management.

Human leukocyte antigens and alloimmunization in heart transplantation: an open debate

Considerable advances in heart transplantation outcome have been achieved through the improvement of donor-recipient selection, better organ preservation, lower rates of perioperative mortality and the use of innovative immunosuppressive protocols. Nevertheless, long-term survival is still influenced by late complications. We support the introduction of HLA matching as an additional criterion in the heart allocation. Indeed, allosensitization is an important factor affecting heart transplantation and the presence of anti-HLA antibodies causes an increased risk of antibody-mediated rejection and graft failure. On the other hand, the rate of heart-immunized patients awaiting transplantation is steadily increasing due to the limited availability of organs and an increased use of ventricular assist devices. Significant benefits may result from virtual crossmatch approach that prevents transplantation in the presence of unacceptable donor antigens. A combination of both virtual crossmatch and a tailored desensitization therapy could be a good compromise for a favorable outcome in highly sensitized patients. Here, we discuss the unresolved issue on the clinical immunology of heart transplantation.