AlloMap Molecular Expression Testing, developed and commercialized by XDx, is a gene expression profiling test that helps doctors identify heart transplant recipients with a low probability of heart transplant rejection.
The AlloMap test is performed using a blood sample, providing doctors with a non-invasive test to help manage the care of patients post transplant. Prior to the availability of AlloMap, the primary method for managing heart transplant rejection was endomyocardial biopsy.
AlloMap test results are reported as a single score, a number from 0-40, with lower scores indicating a lower probability of moderate/severe acute cellular rejection (ACR) at the time the test was performed. The performance characteristics of the AlloMap test make it best suited to help indicate that an acute cellar rejection is not present. The AlloMap score is based on the amount of RNA from each gene in a 20-gene panel comprising of 11 rejection-related genes and 9 genes used for normalization and quality control. Many of the rejection-related genes are associated with biological pathways involved in the immune response and rejection processes.[1]
A clinician uses the AlloMap test score, along with other standard clinical assessments, to evaluate the patient’s probability of acute cellular rejection and the need for additional diagnostic evaluations. AlloMap is not designed to be informative about other forms of heart rejections such as antibody-mediated rejection (AMR) or cardiac allograft vasculopathy (CAV).
AlloMap has been commercially available since 2005 as a CLIA approved Laboratory Developed Test (LDT) and was cleared by the FDA in 2008 as a Class II Medical Device.[2]
The use of the AlloMap test is described in the recommendations for the non-invasive monitoring of acute heart transplant rejection in the first evidence-based clinical practice guidelines for the care of heart transplant recipients issued by the International Society of Heart and Lung Transplantation.[3]
Development
The AlloMap test was developed using genomics and bioinformatics technologies. From approximately 25,000 – 30,000 genes in the human genome, DNA microarrays were used to discover 252 candidate genes for which the amount of RNA in blood samples was related to rejection; called candidate gene expression markers of rejection. Quantitative real-time polymerase chain reaction technology (qRT-PCR) was used to confirm 68 of the candidate genes and to develop the 20-gene AlloMap gene expression panel. The diagnostic performance characteristics of AlloMap testing were verified using independent patient samples obtained from a multicenter clinical study.[4]
Key Clinical Studies
CARGO Study
The development and clinical validation of the AlloMap test used patient samples and clinical data obtained during the Cardiac Allograft Rejection Gene Expression Observational (CARGO) Study. From 2001 to 2005, 737 patients from nine U.S. heart transplant centers enrolled in the CARGO Study and contributed 5,834 blood samples and associated clinical data.[4]
Initial clinical experience at three medical centers was later published in 2006 and the data confirmed the efficacy and performance of the AlloMap test.[5]
IMAGE Study
A comparative effectiveness study, the Invasive Monitoring Attenuation through Gene Expression (IMAGE) Study was designed to compare the clinical outcomes of patients managed with AlloMap to clinical outcomes of patients managed with endomyocardial biopsy. The study included 602 patients from 13 U.S. heart transplant centers who were at least 6 months post-transplant. The study started in 2005 and ended in 2009.
The study results showed that AlloMap was not inferior to endomyocardial biopsy with respect to clinical outcomes when used to monitor stable, asymptomatic heart transplant patients.[6]
Indications for Use
AlloMap Molecular Expression Testing is an In Vitro Diagnostic Multivariate Index Assay (IVDMIA) test service, performed in a single laboratory, assessing the gene expression profile of RNA isolated from peripheral blood mononuclear cells (PBMC). AlloMap Testing is intended to aid in the identification of heart transplant recipients with stable allograft function who have a low probability of moderate/severe acute cellular rejection (ACR) at the time of testing in conjunction with standard clinical assessment.
Indicated for use in heart transplant recipients:
- 15 years of age or older
- At least 2 months (≥55 days) post-transplant
Science and Technology
AlloMap is based on standard quantitative real-time polymerase chain reaction technology (qRT-PCR) using RNA isolated from peripheral blood mononuclear cells (PBMC). A blood sample is collected, PBMC are isolated, lysed and the released RNA stabilized and frozen (PBMC lysate). RNA is then purified from the PBMC lysate. After purification, RNA is converted into complementary DNA (cDNA), and mixed with gene-specific primers and probes. The expression of each gene is then measured by amplification and fluorescence detection using a qRT-PCR instrument. A mathematical classifier combines the measured expression values for each gene into a single value reported as an AlloMap score between 0 and 40.
Each AlloMap score is associated with a Negative Predictive Value (NPV) and a Positive Predictive Value (PPV). AlloMap testing is characterized by high negative predictive values and is therefore a test used to help identify patients at low probability of rejection. The AlloMap test has a relatively low positive predictive value, meaning that even when the AlloMap score is relatively high, the risk of rejection may still be low.
The AlloMap test is performed at the CLIA certified XDx Reference Laboratory in Brisbane, CA.
References
- ^ Dedrick R. Understanding Gene Expression Patterns in Immune-Mediated Disorders. J Immunotox 2007 Jul;4(3):201-7. PMID:18958729
- ^ http://www.accessdata.fda.gov/cdrh_docs/reviews/K073482.pdf
- ^ Costanzo MR et al. The International Society of Heart and Lung Transplantation Guidelines for the care of heart transplant recipients. J Heart Lung Transplant. 2010 Aug;29(8):914-56. PMID: 20643330 http://www.ishlt.org/publications/guidelines.asp
- ^ a b Deng MC, Eisen HJ, Mehra MR, et al. Noninvasive discrimination of rejection in cardiac allograft recipients using gene expression profiling. Am J Transplant 2006;6:150-160. PMID: 16433769
- ^ Starling RC, Pham M, Valantine H, et al. Molecular testing in the management of cardiac transplant recipients: initial clinical experience. J Heart Lung Transplant. 2006 Dec;25(12):1389-95. PMID: 17178330
- ^ Pham, Michael X., Teuteberg, Jeffrey J., Kfoury, Abdallah G., Starling, Randall C., Deng, Mario C., Cappola, Thomas P., Kao, Andrew, Anderson, Allen S., Cotts, William G., Ewald, Gregory A., Baran, David A., Bogaev, Roberta C., Elashoff, Barbara, Baron, Helen, Yee, James, Valantine, Hannah A., the IMAGE Study Group. Gene-Expression Profiling for Rejection Surveillance after Cardiac Transplantation N Engl J Med 2010 0: NEJMoa0912965. PMID: 20413602