Selection and Interpretation of Molecular Diagnostics in Heart Transplantation

Relationship between donor-derived cell-free DNA and tissue-based rejection-related transcripts in heart transplantation

BACKGROUND

Endomyocardial biopsy (EMB)-based traditional microscopy remains the gold standard for the detection of cardiac allograft rejection, despite its limitation of inherent subjectivity leading to inter-reader variability. Alternative techniques now exist to surveil for allograft injury and classify rejection. Donor-derived cell-free DNA (dd-cfDNA) testing is now a validated blood-based assay used to surveil for allograft injury. The molecular microscope diagnostic system (MMDx) utilizes intragraft rejection-associated transcripts (RATs) to classify allograft rejection and identify injury. The use of dd-cfDNA and MMDx together provides objective molecular insight into allograft injury and rejection. The aim of this study was to measure the diagnostic agreement between dd-cfDNA and MMDx and assess the relationship between dd-cfDNA and MMDx-derived RATs, which may provide further insight into the pathophysiology of allograft rejection and injury.

METHODS

This is a retrospective observational study of 156 EMB evaluated with traditional microscopy and MMDx. All samples were paired with dd-cfDNA from peripheral blood before EMB (up to 9 days). Diagnostic agreement between traditional histopathology, MMDx, and dd-cfDNA (threshold of 0.20%) was compared for assessment of allograft injury. In addition, the relationship between dd-cfDNA and individual RAT expression levels from MMDx was evaluated.

RESULTS

MMDx characterized allograft tissue as no rejection (62.8%), antibody-mediated rejection (ABMR) (26.9%), T-cell-mediated rejection (TCMR) (5.8%), and mixed ABMR/TCMR (4.5%). For the diagnosis of any type of rejection (TCMR, ABMR, and mixed rejection), there was substantial agreement between MMDx and dd-cfDNA (76.3% agreement). All transcript clusters (group of gene sets designated by MMDx) and individual transcripts considered abnormal from MMDx had significantly elevated dd-cfDNA. In addition, a positive correlation between dd-cfDNA levels and certain MMDx-derived RATs was observed. Tissue transcript clusters were correlated with dd-cfDNA scores, including DSAST, GRIT, HT1, QCMAT, and S4. For individual transcripts, tissue ROBO4 was significantly correlated with dd-cfDNA in both nonrejection and rejection as assessed by MMDx.

CONCLUSIONS

Collectively, we have shown substantial diagnostic agreement between dd-cfDNA and MMDx. Furthermore, based on the findings presented, we postulate a common pathway between the release of dd-cfDNA and expression of ROBO4 (a vascular endothelial-specific gene that stabilizes the vasculature) in the setting of antibody-mediated rejection, which may provide a mechanistic rationale for observed elevations in dd-cfDNA in AMR, compared to acute cellular rejection.

Myocarditis in children 2024, new themes and continued questions

PURPOSE OF REVIEW

While pediatric myocarditis incidence has increased since the coronavirus disease 2019 (COVID-19) pandemic, there remain questions regarding diagnosis, risk stratification, and optimal therapy. This review highlights recent publications and continued unanswered questions related to myocarditis in children.

RECENT FINDINGS

Emergence from the COVID-19 era has allowed more accurate description of the incidence and prognosis of myocarditis adjacent to COVID-19 infection and vaccine administration as well that of multi-system inflammatory disease in children (MIS-C). As cardiac magnetic resonance technology has shown increased availability and evidence in pediatric myocarditis, it is important to understand conclusions from adult imaging studies and define the use of this imaging biomarker in children. Precision medicine has begun to allow real-time molecular evaluations to help diagnose and risk-stratify cardiovascular diseases, with emerging evidence of these modalities in myocarditis.

SUMMARY

Recent information regarding COVID-19 associated myocarditis, cardiac magnetic resonance, and molecular biomarkers may help clinicians caring for children with myocarditis and identify needs for future investigations.

Surveillance with dual noninvasive testing for acute cellular rejection after heart transplantation: Outcomes from the Surveillance HeartCare Outcomes Registry

BACKGROUND

Molecular testing with gene-expression profiling (GEP) and donor-derived cell-free DNA (dd-cfDNA) is increasingly used in the surveillance for acute cellular rejection (ACR) after heart transplant. However, the performance of dual testing over each test individually has not been established. Further, the impact of dual noninvasive surveillance on clinical decision-making has not been widely investigated.

METHODS

We evaluated 2,077 subjects from the Surveillance HeartCare Outcomes Registry registry who were enrolled between 2018 and 2021 and had verified biopsy data and were categorized as dual negative, GEP positive/dd-cfDNA negative, GEP negative/dd-cfDNA positive, or dual positive. The incidence of ACR and follow-up testing rates for each group were evaluated. Positive likelihood ratios (LRs+) were calculated, and biopsy rates over time were analyzed.

RESULTS

The incidence of ACR was 1.5% for dual negative, 1.9% for GEP positive/dd-cfDNA negative, 4.3% for GEP negative/dd-cfDNA positive, and 9.2% for dual-positive groups. Follow-up biopsies were performed after 8.8% for dual negative, 14.2% for GEP positive/dd-cfDNA negative, 22.8% for GEP negative/dd-cfDNA positive, and 35.4% for dual-positive results. The LR+ for ACR was 1.37, 2.91, and 3.90 for GEP positive, dd-cfDNA positive, and dual-positive testing, respectively. From 2018 to 2021, biopsies performed between 2 and 12-months post-transplant declined from 5.9 to 5.3 biopsies/patient, and second-year biopsy rates declined from 1.5 to 0.9 biopsies/patient. At 2 years, survival was 94.9%, and only 2.7% had graft dysfunction.

CONCLUSIONS

Dual molecular testing demonstrated improved performance for ACR surveillance compared to single molecular testing. The use of dual noninvasive testing was associated with lower biopsy rates over time, excellent survival, and low incidence of graft dysfunction.

De Novo Donor-Specific Antibodies after Heart Transplantation: A Comprehensive Guide for Clinicians

Antibodies directed against donor-specific human leukocyte antigens (HLAs) can be detected de novo after heart transplantation and play a key role in long-term survival. De novo donor-specific antibodies (dnDSAs) have been associated with cardiac allograft vasculopathy, antibody-mediated rejection, and mortality. Advances in detection methods and international guideline recommendations have encouraged the adoption of screening protocols among heart transplant units. However, there is still a lack of consensus about the correct course of action after dnDSA detection. Treatment is usually started when antibody-mediated rejection is present; however, some dnDSAs appear years before graft failure is detected, and at this point, damage may be irreversible. In particular, class II, anti-HLA-DQ, complement binding, and persistent dnDSAs have been associated with worse outcomes. Growing evidence points towards a more aggressive management of dnDSA. For that purpose, better diagnostic tools are needed in order to identify subclinical graft injury. Cardiac magnetic resonance, strain techniques, or coronary physiology parameters could provide valuable information to identify patients at risk. Treatment of dnDSA usually involves plasmapheresis, intravenous immunoglobulin, immunoadsorption, and ritxumab, but the benefit of these therapies is still controversial. Future efforts should focus on establishing effective treatment protocols in order to improve long-term survival of heart transplant recipients.