Study confirms VirtualPhenotype™ can predict response to HIV therapy from genetic resistance information

September 19, 2000

Test may fulfill need for standardized interpretation

TORONTO, ONTARIO, September 20, 2000 - Results presented today at the 40th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) indicate that the VirtualPhenotype™, Virco's new automated HIV drug resistance test, can predict response to therapy from genetic information with comparable results to a panel of international experts.

"This study confirms that genotypic resistance information with sophisticated interpretation, such as that provided by the Virtual Phenotype or our panel of expert clinicians, is a useful predictor of response to therapy and significantly better than relying on the treatment history, which can be misleading," commented lead investigator Dr. Victoria Johnson of the University of Alabama, Birmingham, in collaboration with the University of Alabama HIV database program under the direction of Dr. Michael Saag. "This adds to the growing weight of evidence supporting the clinical utility of resistance testing."

In the study, the use of interpreted genotypic resistance information was highly predictive of the patient's response to therapy. This contrasted with use of the treatment history of each patient (the information on which treatment decisions have been made prior to the development of HIV drug resistance testing), which was found not to be predictive of treatment response.

The study compared the "proportional hazard" of virologic failure if the expert or VirtualPhenotype™ predicted susceptibility to the drug in question. The results for each of the experts, for all combined and for VirtualPhenotype™ were 0.71, 0.70, 0.75, 0.65, 0.67 and 0.69 respectively. All except Expert 3 were significantly predictive of outcome (p<0.05).

The study also revealed differences between the interpretation of different experts, highlighting the need for standardization of genotypic interpretation to ensure optimal treatment decision-making.

"Given the complexity of HIV drug resistance, only a relatively small number of experts can undertake interpretation of genotypic information with real confidence and the virtual phenotype represents a viable and reliable alternative for standardized interpretation of genotypic information," adds Dr. Johnson.

HIV genotyping involves reading the genetic code to detect where mutations have occurred that could confer resistance to one or more of the 15 HIV drugs currently available. The chief limitation of this approach is that there are over 100 mutations that can interact and counteract one another in highly complex ways to cause resistance. This makes the interpretation of raw genotypic resistance information extremely difficult, which underscores the need for standardization of the interpretation.

Historically, the only alternative to genotyping has been phenotyping where the virus is derived from the patient's blood sample and grown in the presence of varying concentration of all the available drugs in the laboratory. This is more complex to perform and requires more time than genotyping.

Virco's solution to this is a new, third approach to HIV drug resistance monitoring - the VirtualPhenotype™. First the genetic code is read and all the resistance mutations detected. These data are then entered into Virco's computerized system that searches the World's largest database of approximately 100,000 genotypes and phenotypes for samples with the same patterns of mutations. Once these are found, the system retrieves the corresponding phenotypes for these samples (typically thousands per drug) and calculates the average resistance score for each drug. The VirtualPhenotype™ provides the highest quality of interpretation with a quantitative estimate of resistance to each drug available to all physicians.

Data presented earlier this year demonstrated that the VirtualPhenotype™ is highly predictive of actual phenotypic drug resistance and of treatment response, and superior to other current interpretation systems that interrogate simplified resistance tables or 'rules' to predict resistance.
Virco is a multinational biotechnology company with facilities in the United States, the United Kingdom, Belgium 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 genotyping, phenotyping and the new, unique VirtualPhenotype™for testing HIV drug resistance. The company believes it provides the most sophisticated and comprehensive portfolio of HIV drug resistance monitoring and decision support tools for physicians treating HIV infected patients.

Virco sells its testing services via Laboratory Corporation of America Holdings (LabCorp), SRL in Japan, as well as directly to HIV/AIDS centres in Europe, Canada, Australia and other countries around the world. Virco has a two-year agreement with Gilead Sciences 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:

Cooney Waters Group, Inc.

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