The U.S. blood-testing market received a shot in the arm with news of FDA approval for the Procleix HIV-1/HCV Assay and the Procleix Semi-Automated System, a nucleic acid test system that detects viral genes rather than antibodies for screening donors.

Gen-Probe Inc. received FDA approval of its biologics license application for the amplified nucleic acid test to be used by blood banks to simultaneously detect human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV). The Procleix HIV-1/HCV Assay and the Procleix Semi-Automated System will be marketed worldwide by Chiron Corp. as part of a July 1998 deal.

“Chiron could have done a deal with a number of other companies,” Gen-Probe CEO Henry Nordhoff said. “But in looking at our technology and our track record of successfully introducing products of this type, we decided to do a deal together. I think it’s really a validation of our basic array of technologies, many of which are components of the Procleix assay and system.”

Gen-Probe expects to immediately profit from the news.

“This will be very important for the company,” Nordhoff said. “We see in a few years the revenues from blood screening comprising about half of total revenues.”

The combination HIV-1/HCV test system was developed and manufactured by San Diego-based Gen-Probe, which also received 510(k) clearance for the Procleix Semi-Automated Instrument System and the HIV-1/HCV External Quality Controls Kit.

Specific terms of the original revenue-sharing agreement were not disclosed.

“Gen-Probe was responsible for the clinical development as well as the manufacturing,” Nordhoff said. “We then transfer it to Chiron, which is responsible for the marketing, selling and distribution of it. This is the way it’s been working out for two-and-a-half years. The big difference now is that it is an approved test and we can charge a commercial price.”

Emeryville, Calif.-based Chiron was a logical partner for the screening test because of its current broad HCV testing patent portfolio.

“The immunoassays we currently have in place are state of the art in terms of detecting antibodies,” said Bruce Phelps, Chiron’s vice president of research and development. “These are the key tests now to actually detect the virus itself. So they significantly close what we call the window period’ between the time of infection and the time these infectious agents can be detected. So it supplements and complements the immunoassay tests we have very nicely.”

The assay’s early clinical testing involved its use beginning in March 1999 under an investigational new drug protocol with the American Red Cross, with which Gen-Probe has an exclusive relationship to use its amplified DNA probe test for screening.

“Over the years we’ve expanded that [IND protocol] to 10 sites that cover about 70 percent of the whole blood market in the U.S.,” said Larry Mimms, Gen-Probe’s vice president for development of blood products.

The expanded screening includes America’s Blood Centers affiliates, the Association of Independent Blood Centers and the U.S. military. During this period, more than 24 million donations were screened. Ninety-five donations were identified as positive for either HIV or HCV, preventing these blood units from entering the blood supply.

The assay uses a family of technologies including a nucleic acid amplification technique called Transcription-Mediated Amplification, which amplifies the genetic contents of each specific virus to detect infection significantly earlier.

In contrast, current tests are enzyme-immunoassays, which involve detecting antibodies. But these tests cannot detect a virus during the time required for the donor to develop an immune response, leaving open the door for potential slip-ups in the screening process. It can take up to 22 days to find detectable antibodies for HIV, and up to 80 days or more for HCV.

“Someone could be infected today, and then donate blood a week later, and while the viruses are in the blood, the person receiving the blood will be infected,” Nordhoff said. “The enzyme-immunoassay test will not pick that blood as being infected because the antibodies aren’t there. The advantage of our test is we detect the virus directly. The take-home message is that the blood supply is safer because the seroconversion window is shortened rather substantially.”

Gen-Probe said its test reduces the detection time by about 50 percent for HIV and by 70 percent or more for HCV.

The company plans to further its testing platform to include detection of hepatitis B, hepatitis A and parvovirus B19. Chiron will continue to be involved as a partner in developing further blood supply tests.