Clinical usefulness of gene-expression profile to rule out acute rejection after heart transplantation: CARGO II

Abstract

Aims: A non-invasive gene-expression profiling (GEP) test for rejection surveillance of heart transplant recipients originated in the USA. A European-based study, Cardiac Allograft Rejection Gene Expression Observational II Study (CARGO II), was conducted to further clinically validate the GEP test performance.

Methods and results: Blood samples for GEP testing (AlloMap(®), CareDx, Brisbane, CA, USA) were collected during post-transplant surveillance. The reference standard for rejection status was based on histopathology grading of tissue from endomyocardial biopsy. The area under the receiver operating characteristic curve (AUC-ROC), negative (NPVs), and positive predictive values (PPVs) for the GEP scores (range 0-39) were computed. Considering the GEP score of 34 as a cut-off (>6 months post-transplantation), 95.5% (381/399) of GEP tests were true negatives, 4.5% (18/399) were false negatives, 10.2% (6/59) were true positives, and 89.8% (53/59) were false positives. Based on 938 paired biopsies, the GEP test score AUC-ROC for distinguishing ≥3A rejection was 0.70 and 0.69 for ≥2-6 and >6 months post-transplantation, respectively. Depending on the chosen threshold score, the NPV and PPV range from 98.1 to 100% and 2.0 to 4.7%, respectively.

Conclusion: For ≥2-6 and >6 months post-transplantation, CARGO II GEP score performance (AUC-ROC = 0.70 and 0.69) is similar to the CARGO study results (AUC-ROC = 0.71 and 0.67). The low prevalence of ACR contributes to the high NPV and limited PPV of GEP testing. The choice of threshold score for practical use of GEP testing should consider overall clinical assessment of the patient's baseline risk for rejection.

Trial registration: ClinicalTrials.gov NCT00761787.

Keywords: AlloMap; Heart transplant; Molecular diagnostics; Organ rejection; Rejection surveillance; Tests.

Figure 1

Source of patients and samples included in the area under the receiver operating characteristic curve calculations and modelling of negative predictive value (NPV) and positive predictive value (PPV) performance of gene-expression profiling in the study population. Local biopsy (and pathology grading): local centre's pathologist's grade of rejection of an endomyocardial biopsy and a paired blood sample for gene-expression profiling available for the patient visit. Central pathology review: a central panel of pathologists provided independent grading of rejection of the endomyocardial biopsy slides and a paired blood sample for gene-expression profiling available for the patient visit. Note: the negative predictive value and positive predictive value calculations used the local biopsy findings to adjust for prevalence rates for rejection. The central biopsies were used to ascertain the reference standards for Grade 3A or more severe rejection grades vs. lesser grades of rejection.

Figure 2

Gene-expression profiling score by the time post-transplant. The number of gene-expression profiling tests between Month 12 and Month 13 post-transplant ranged from 24 (Month 11) to 128 (Month 3). The number of gene-expression profiling tests between Month 14 and Month 24 post-transplant ranged from 2 (Month 24) to 11 (Month 15).