Recent data from the Lung Allograft Rejection Gene expression Observational (LARGO) study provides compelling evidence that profiling gene expression in peripheral blood can detect organ rejection in lung transplant patients.
Data from the study shows that the immune responses of lung transplant recipients can result in novel molecular signatures identifying the absence or presence of acute cellular rejection (ACR). That molecular signature can be identified using the quantitative real-time polymerase chain reaction (RT-PCR), a technology that measures the intracellular RNA levels of individual genes.
By distinguishing the patterns of gene expression in white blood cells (leukocytes), which fluctuate during the rejection of foreign tissue, PCR-based gene profiling can identify individual genes and pathways associated with the rejection status of transplanted lungs. In addition, the study shows that some of the genes whose expression changes during rejection of a transplanted lung are the same as those whose expression changes during the rejection of a transplanted heart.
Using microarray analysis, the researchers identified 259 genes that were differentially expressed for A0 and >A2 rejection grades (based on a standardized severity scale of 0-4). RT-PCR confirmed 14 of these genes as candidates for analysis, revealing a high correlation with those identified using microarray analysis. Seven of those genes were considered statistically significant.
"We are excited to confirm that new monitoring methods, such as non-invasive blood tests that determine a patient's gene expression profile, can identify those genes that are expressed during the rejection of a lung," said Shaf Keshavjee, M.D., Chair, Division of Thoracic Surgery, University of Toronto, and LARGO study lead. "The data being presented at this year's ISHLT meeting shows the potential that exists to develop a non-invasive test that could alleviate the need for tens of thousands of biopsies."
Currently, uncomfortable and invasive biopsies are the standard for monitoring lung transplant recipients for acute cellular rejection. Biopsies are performed frequently in the first year post-transplant and periodically thereafter, often for the patient's lifetime.
Current data shows that 1,400 lung transplants were performed in 2006. And in recent years, approximately 83.3 percent of lung transplant patients survived one year following the transplant, while 62.8 percent survived three years and 47.3 survived five years. Transplant rejection is a primary concern for long-term survival, both immediately after surgery and through the patient's lifetime. To prevent rejection and subsequent damage to the new lungs, patients must take a lifelong regimen of immunosuppressive drugs.
"Refining the Identification of Discriminatory Genes for Rejection in Lung Transplantation: The LARGO Study" will be presented today by Shaf Keshavjee, M.D., Chair, Division of Thoracic Surgery, University of Toronto, and LARGO study lead at the 27th Annual Meeting and Scientific Sessions of the International Society for Heart and Lung Transplantation (ISHLT).