News Release

XDx to present recent success with AlloMap molecular expression testing

at American Transplant Congress 2007

Peer-Reviewed Publication

HealthStar PR

San Francisco, CA, May 7, 2007 -- XDx, a molecular diagnostics company, today announced its AlloMap® molecular expression test will be the subject of presentations and discussions at the American Transplant Congress 2007 held here, May 5 to 9.

The test, currently used to detect the absence of heart transplant rejection instead of routine invasive heart muscle biopsies, has now been shown to correlate with oxygen saturation levels, cardiac filling pressures, and the electrical properties of the transplanted heart. Also, data from the Lung Allograft Rejection Gene expression Observation (LARGO) study presented at the ATC sessions demonstrate that a non-invasive blood test can detect cytomegalovirus-induced immune responses in lung transplant patients.

"These data continue to validate the outcomes of the Cardio Allograft Gene Expression Observational (CARGO) and LARGO studies and demonstrate how non-invasive molecular expression testing can be used clinically," said Mario C. Deng, M.D., director of Cardiac Transplantation Research, Columbia University Medical Center/New York-Presbyterian Hospital, and co-principal investigator in the Cardiac Allograft Gene Expression Observational (CARGO) study. "For the 21,000 U.S. heart transplant patients undergoing an estimated 40,000 heart muscle biopsies each year, a non-invasive test is a welcome alternative."

In separate studies, recent data from the CARGO study show that the non-invasive AlloMap molecular test may help reduce the use of immunosuppressants without the need for invasive biopsies and can serve to measure heart graft blood flow and blood pressure.

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More information on ATC can be found at www.atcmeeting.org.

About XDx

XDx's mission is to improve patient care by developing molecular diagnostics that translate an individual's immune status into clinically actionable information. Founded in 2000, XDx is a molecular diagnostics company that utilizes state-of-the-art genomic technology and sophisticated bioinformatics analyses to understand and measure the immune processes that underlie specific immune-mediated conditions. Physicians can use this information to optimize patient treatment and minimize the long-term consequences of immunosuppressive therapies.

XDx's science and technology is now being evaluated in patients with solid organ transplants. Building on the discoveries made during the development of AlloMap testing for heart transplant patients, which included the identification of many genes and pathways involved in tissue rejection, XDx is now developing a product for use by physicians to better manage lung transplant patients. Beyond the use of AlloMap testing in assessing immune response in solid organ transplantation, XDx scientists are applying similar approaches to create new molecular diagnostic tests for the improved clinical management of immune-mediated inflammatory diseases, such as systemic lupus erythematosus (SLE or lupus,) to diagnose and predict clinical flares common in a variety of these diseases.

In addition to its potential for use by physicians for better patient management, the XDx approach is of interest to pharmaceutical companies looking to use biomarkers predictive of drug efficacy in order to proactively identify patient response and to better target their drug development efforts and clinical trials.

More information can be found at www.xdx.com.

About AlloMap Molecular Expression Testing

The first product using this unique approach is AlloMap molecular expression testing. This service, offered through the XDx CLIA-certified clinical laboratory since January 2005, is being used by a number of leading cardiac transplant centers in the United States to monitor patients following their heart transplants. The scientific and clinical validation of this technology has been described in a peer-reviewed article published in the American Journal of Transplantation. More information can be found at www.allomap.com.

CONTACT
Corporate:
Debbie Frantz
XDx
415-287-2300
415-287-2301

Dave Schemelia
HealthStar Communications
646-722-8819


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