Pivotal Clinical Trial Begins for Procleix West Nile Virus Blood Screening Assay; Ongoing Screening Already Has Intercepted 20 WNV-Infected Blood Donations

SAN DIEGO and EMERYVILLE, Calif. -- Gen-Probe and Chiron  announced today that the pivotal clinical trial of the companies' Procleix West Nile virus (WNV)

blood screening assay has been initiated.

The companies also noted that since the start of this year's mosquito season in May, ongoing screening of the U.S. blood supply with the Procleix WNV Assay, labeled for investigational-use only, has detected 20 WNV-infected

donations to date, thereby preventing transfusion of virally contaminated blood into as many as 60 blood recipients.  These WNV-infected donations have been detected from donors in Arizona, California, New Mexico and Louisiana.

Since July of 2003, the Procleix WNV Assay has been used nationwide to screen the U.S. blood supply for WNV under an investigational new drug application (IND).

"West Nile virus continues to increase as a health concern as the virus spreads across the United States," said Andrew Heaton, MD, vice president and chief medical officer at Chiron Blood Testing. "Chiron is committed to increasing the safety of the blood supply, and we are hopeful that the Procleix WNV Assay will be an important advance in addressing this new health threat."

"Beginning this pivotal trial on schedule and in time for the peak

mosquito season is another important milestone in what has been a remarkably rapid development program to address an emergent health-care concern," said Jim Godsey, PhD, Gen-Probe's executive vice president of development.  "We

remain on track with plans to file a Biologics License Application (BLA) to commercialize the West Nile virus Assay in the first quarter of 2005."

The pivotal clinical trial, which is being conducted at five U.S. blood

centers, will evaluate the Procleix WNV Assay's sensitivity, specificity and reproducibility on the semi-automated instrumentation platform called eSAS.

Blood will be tested in pools of 16 and individually in the trial, which is expected to last approximately four months.

Gen-Probe and Chiron expect to begin IND testing of the Procleix WNV Assay

in August on the fully automated, high-throughput TIGRIS amplified nucleic

acid testing (NAT) instrument.  The TIGRIS system is expected to increase the

efficiency of testing individual blood donations.  Testing individual

donations enables more sensitive detection of WNV, which is often present only

in small numbers in blood.

At last week's annual congress of the International Society of Blood

Transfusion (ISBT) in Edinburgh, Gen-Probe researchers presented data that

showed "excellent comparability" between the Procleix WNV Assay results on the

eSAS and TIGRIS systems.

WNV is a mosquito-borne virus associated with a human form of the disease

ranging from mild, flu-like symptoms to severe neurological disease.  The

first confirmed U.S. death resulting from transmission through donated blood

was reported in 2002.  In the fall of 2002, the Food and Drug

Administration (FDA) challenged industry to develop a test for direct detection of

WNV in donated blood by the summer of 2003.  Within nine months, Gen-Probe and

Chiron had developed the Procleix WNV Assay and brought it to market under an

IND.  According to the U.S. Centers for Disease Control and Prevention, 108

human cases of WNV infection have been reported for the current mosquito

season as of July 13, 2004.

Source: Chiron