Originally Published IVD Technology January/February 2003
INDUSTRY NEWS
Manufacturers rush to develop WNV assay |
| FDA hopes to have a WNV test available before the onset of mosquito season. |
IVD manufacturers are scrambling to develop rapid and effective nucleic acid tests to screen donated blood for West Nile virus (WNV) before the onset of mosquito season this summer. Although the virus may lie dormant in 2003, FDA will require WNV screening of the entire blood supply. In 2002, the United States' WNV epidemic escalated to a final count of 3873 confirmed cases and 246 deaths, with 13 cases having been confirmed and 20 under investigation for blood transfusion-related transmissions. The disease can easily be passed into the blood supply because 80% of infected people are asymptomatic, and would therefore possibly qualify to donate blood.
FDA will promote an extensive multisite study of candidate WNV tests under an investigational new drug (IND) exemption. The agency will select a specific antibody assay, such as the immunoglobulin M test, as the standard confirmatory assay by which to measure the sensitivity of the nucleic acid tests, the chosen platform for the test.
According to Jesse Goodman, MD, director of the Center for Biologics Evaluation and Research (CBER), the key to a successful new test will be sensitivity and accuracy. In a meeting of AdvaMed (Washington, DC), the American Association of Blood Banks (AABB), CBER, and CDC in September 2002, FDA announced that its early guidelines for analytical sensitivity were 100 copies/ml to ensure 100% detection of 1000 copies or genomic equivalence per milliliter sample. CBER will establish further performance criteria and standards.
FDA will be as flexible as possible to help facilitate the rapid development of a test. They might even consider widespread use of a test while research is ongoing. However, the tight time frame is only one of many obstacles that stand in the way of the rapid development of a suitable assay.
"One of the most sorely lacking areas is the specimens from the presymptomatic phase of infection," says George Dawson of Abbott Laboratories (Abbott Park, IL). "These are exactly the type of samples that are needed to develop blood-screening tests. So, there is a real lack of having the correct specimens to make the right conclusions about the assay formats and their needed sensitivity."
James Gallarda director of blood screening development at Roche Molecular Diagnostics (Alameda, CA) agrees, "I think we are targeting the preseroconversion window period." Gallarda says there is a need for preseroconversion panels to help assess the level of viremia and the duration of the window period, which may last anywhere from a few days to two weeks.
"One preparation of virus can behave completely differently than another," says Gallarda, "so it will be very important to have FDA develop a set of panels that can be used as reference panels to allow manufacturers to target the development of a system in the way that should be uniform."
In December, Boston Biomedica (West Bridgewater, MA) released a set of panels for use in the research and development of a test. the panel consisted of 12 positive members from 10,000 to 30 copies/ml of WNV RNA and 3 negative members.
During the window period immunoassays, the technology currently used to test for WNV, could produce false-negative results causing blood banks to discard too much usable blood.
According to Goodman, serological testing is inadequate as the sole WNV testing platform. "In general, it looks like if you get antibody, it's not long after that that you clear the virus from your blood." However, such tests can be used to screen blood going to high-risk patients, until a nucleic-acid-based assay is developed.
Nucleic acid tests offer high specificity, but low sensitivity when testing for a low concentration of virus, thereby threatening a false-negative result. "The viral yield for this infection is much lower than what we have seen for HCV, HIV, or HBV," says Dawson. This low viremia makes it very unlikely that pooled blood testing, as is standard for HIV and HCV testing, will be sensitive enough to reliably detect WNV-positive samples. However, the AABB says that there are very few places in the country that are able to do single-donation testing. Blood centers are therefore relying on the ability of manufacturers to improve the sensitivity of nucleic acid testing.
One solution to the lack of sensitivity is target amplification. According to Glen Freiberg, vice president for regulatory, clinical, and quality systems at Gen-Probe Inc. (San Diego), the company's "assay will use target capture, transcription-mediated amplification, and a hybridization protection assay for protection." This method has proven successful; initial studies indicate a 95% detection rate at 10 copies/ml of WNV. Gen-Probe expects to have the test available for distribution to blood banks for screening by the mddle of 2003.
Manufacturers have also used signal amplification to improve sensitivity. Cygene (Coral Springs, FL) has confronted the obstacle of low-viral yield with its front-end haystack processing technique. Martin Munzer, the company's president explains that it has been "focusing its efforts on detection methods based on signal amplification post target isolation." This technique involves protection of the target protein and removal of all unwanted protein. A molecular beacon is then used to detect the target. The company hopes to have its assay available for review by FDA by spring and possible distribution by summer.
Several manufacturers have found the challenge of forging the path to rapid assay development an opportunity for growth. Freiberg views this as an opportunity for industry and government to reexamine the CBER licensing process. He says, "the controls on manufacturing should resemble the CDRH PMA process rather than a traditional CBER therapeutic process. While CBER has converted to the device GMPs, there are still significant restrictions on how CBER-regulated IVDs are manufactured and improved." Munzer views WNV assay development as an opportunity for his company to make a name for itself. "This is a small company. If we can get this patent, it should put us on the map with respect to the IVD industry."
Successful development of an assay will yield substantial financial return. Jim MacPherson, chief executive of America's Blood Centers (Washington, DC) estimates that a WNV assay cleared for investigational use only will yield $5–$7 per test in revenue for the manufacturer, and this yield is likely to double that once full licensure is granted. Ultimately, WNV testing could provide a an estimated $200 million annual market for the manufacturers.
However, this profit may be short-lived. A WNV vaccine is currently under development, which may protect the blood supply from contamination by WNV and eventually minimize the need for an assay. This spring, Acambis Inc. (Canton, MA) expects to begin phase I trials of its WNV vaccine, and estimates that it will be a minimum of three years after the completion of these trials before the vaccine can be released on the market. Until then, FDA expects an assay to be the best containment technique.
Assay developers do not feel threatened by the vaccine. It "may take a while to saturate the public, even longer to saturate the blood supply, and may never be applicable for immunocompromized individuals," says Munzer.
Vitex (Watertown, MA) plans to take another approach to reducing the threat of WNV by developing a virus inactivation system for eliminating WNV in red blood cells. In December, Vitex began its Phase III clinical trials, and estimates that its product will likely reach the U.S. market in mid-2005. However, the effectiveness and safety of this process has yet to be determined.
The WNV test-development process will serve as the example for rapid response in the future. Goodman believes that WNV test development "is a test of flexibility and agility for the blood industry, for the diagnostics industry, and certainly for FDA. [We should] learn lessons from the present. These are relevant to future emerging infectious diseases, of which there shall be more, and also to the unfortunate potential for bioterrorism."
With four confirmed cases of organ donation–related WNV transmission to date, FDA is also interested in developing tests to screen donated tissues and organs for the virus for which serologically based tests, ELISA, and plaque reduction neutralization will be used rather than nucleic-acid-based techniques.
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