Next-generation 'virtual' HIV drug resistance testing now available

May 21, 2000

VirtualPhenotype™ Links Genotype to Phenotype Data for Improved Quantitative Prediction of Drug Resistance

BALTIMORE, MD, May 22, 2000 -- VirtualPhenotype™, a powerful new quantitative approach to HIV resistance testing, is now available in the U.S. via Laboratory Corporation of America® Holdings (LabCorp®) (NYSE: LH), Virco announced today. The greatly enhanced system, developed by Virco, uses the company's proprietary interpretation software to interrogate the world's largest database of resistance information and predict which drugs the patient's HIV will respond to and which it will be able to resist, based on the genetic code of their virus. This approach, which represents one of the world's first working examples of pharmacogenomics (the science that uses genomic information to individualize patient pharmaceutical treatment), is already proving to be a major step forward in the interpretation of HIV resistance.

"By tapping into such a large database, the virtual phenotype will allow the matching of a patient's HIV to thousands of other examples that are genetically similar in order to make the most accurate prediction of resistance possible," says John Mellors, M.D. of the University of Pittsburgh Medical Center. "This is likely to improve the accuracy of interpretation of HIV resistance genotypes and, consequently, treatment decisions that are based on genotypic testing," predicts Dr. Mellors.

HIV/AIDS mutates very readily as it replicates and any mutants that are resistant to drug therapy can swiftly become the dominant strain. This is one of the main causes of HIV treatment failure. Resistance information can be used to help select the optimal combination of drugs for the individual patient.

Currently, two main approaches are used to assess HIV drug resistance in a patient. One method examines the ability of the virus to replicate in the presence of each of the available drugs and is a direct measure of resistance - the phenotype. The other approach is to 'read' the genetic code of the patient's virus - the genotype. This reveals which 'letters' of the code have mutated. However, given the existence of over 100 mutations known to cause HIV drug resistance, the interpretation of genotypic data can often be extremely complex.

The next-generation Virco test addresses this challenge by firstly analysing the patient's genotype, then searching the company's database of over 65,000 HIV samples for previous genotypes with the same patterns of mutations. It then retrieves the phenotypes that correspond to these samples, averages the information for each drug and predicts to which drugs the current sample will be sensitive or resistant. This is called the VirtualPhenotype.

An analysis of over 10,000 patient samples showed that the VirtualPhenotype is highly reliable, with discordance between the VirtualPhenotype and the real phenotype in less than 1% of cases. Additional data also shows that the VirtualPhenotype can be more reliable than the current 'rule-based' interpretation approaches that simply use lists of mutations for each drug to predict resistance or sensitivity.

"This is the first quantitative interpretation of the genotype and we hope and expect that it will prove to be a valuable new tool to help physicians provide the most effective, individualised therapy to their patients. We are pleased with this new milestone and are committed to continuing to advance the system's capabilities," says Brendan Larder, Ph.D., Vice President of Research and Development of the Virco Group. "For example, we are now conducting research using artificial intelligence so that the Virtual/Phenotype system will be able to learn as it goes along and even identify new mutations and combinations of mutations that affect resistance."

Company Background
Virco is a multinational biotechnology company with operating subsidiaries in the United States, Belgium, The United Kingdom and Ireland. It applies the most advanced technologies in molecular biology, automation, ultra high-throughput screening and electronic data processing to the diagnosis and management of HIV, other infectious diseases and cancer. Virco is the only company to provide both genotyping and phenotyping HIV drug resistance testing and believes it provides the most sophisticated and comprehensive portfolio of phenotyping and genotyping decision support tools for physicians treating HIV infected patients. Virco sells its testing services via Laboratory Corporation of America Holdings (LabCorp) as well as directly to HIV/AIDS centres in Europe, Canada, Japan and Australia. Virco has also recently announced a two-year agreement with Gilead for the promotion of Virco Resistance Monitoring Services to US HIV Prescribers by the Gilead sales force. For further information, please visit Virco's website: http://www.vircolab.com.
-end-
Note to editors:

VirtualPhenotype™ is a trademark of the Virco Group and is the new genotypic interpretation product from Virco.

VircoGEN II™ is Virco's inclusive genotyping service, which comprises sequencing of viral genetic material, identification of all the point mutations associated with resistance and VirtualPhenotype™ interpretation.

Antivirogram™ is Virco's phenotyping service.

Cooney Waters Group, Inc.

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