PARIS ¿ The Belgian company Tibotec-Virco NV presented results of a study showing that Virco resistance tests can predict clinical response to HIV treatment for up to two years.

The Mechlen-based company claimed this is the first evidence of the long-term benefits of resistance testing, since previous studies had typically lasted only 16 to 24 weeks.

The study, carried out on 681 HIV-positive patients being treated by the Chelsea and Westminster Hospital HIV Clinic in London, entailed the use of Virco¿s proprietary VirtualPhenotype and Antivirogram resistance tests to estimate the number of drugs to which each patient¿s virus was still susceptible over a 96-week period. The viral load and CD4 cell counts were then compared for patients receiving none, one, two, three or four active drugs.

The two tests were found to be equal and highly significant predictors of outcomes over 96 weeks. Patients receiving three or four active drugs experienced significantly greater reductions in viral load and increases in CD4 cell count during the period of the study, and a higher proportion saw their viral loads fall to undetectable levels.

It also was found that patients who changed therapy at the time of the testing experienced a ¿vastly superior response compared to those who did not.¿ Almost 80 percent of patients who changed therapy when undergoing resistance testing received three or four active drugs, compared with just 23 percent of those who did not change.

Because HIV has the ability to develop mutant strains that are resistant to therapies, drug resistance testing helps physicians select the most effective of the 15 HIV drugs currently available to tailor a combination therapy for the patient. HIV drug resistance tests have traditionally been based on one of two approaches ¿ phenotyping (a direct measure of resistance) or genotyping (reading the patient¿s genetic code to detect where mutations have occurred that could confer resistance) ¿ but the Virco VirtualPhenotype test is based on a third approach that combines both techniques.

It starts by reading the patient¿s genetic code and detecting all resistant mutations. The data are fed into Virco¿s computer system, which searches the world¿s largest database of some 100,000 genotypes and phenotypes for virus samples with the same mutation patterns. The system retrieves the corresponding phenotypes for the mutations found in the patient (typically thousands for each drug) and calculates the average resistance score for each drug. It thus produces a quantitative estimate of the patient¿s resistance to every available drug.

Tibotec-Virco was created through the merger of Virco Group NV (drug discovery and development) and Tibotec Group NV (pharmacogenomics and molecular diagnostics) in March, and has direct subsidiaries in the UK, Ireland and the U.S. It sells its resistance testing services under the Virco name through various distributors. The company also is developing genomics-based diagnostic tests for hepatitis and cancer, while its drug discovery activities are focused on the development of HIV drugs that are active against resistant strains of the virus.

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