The retrospective study of 681 HIV-positive patients receiving care from the Chelsea and Westminster Hospital HIV Clinic, London, UK used the VirtualPhenotype? and Antivirogram? resistance tests to estimate the number of drugs to which each patient's virus was still susceptible (the number of active drugs). The viral load and CD4 cell counts were then compared for patients receiving 0, 1, 2, 3 or 4 active drugs. Both tests were found to be equally and highly significant predictors of outcome over 96 weeks. Patients receiving three or four active drugs experienced significantly greater reductions in viral load and increases in CD4 cell counts over the 96-week study, and a greater proportion achieved undetectable viral loads.
"The results of this study of HIV patients in our clinic indicate that resistance testing can be useful in helping physicians select the optimum combination of drugs for each patient, thereby maximizing their response to treatment over the long-term," said Professor Brian Gazzard, Consultant Physician and Director of HIV Research, Chelsea and Westminster Hospital HIV Clinic, London, UK.
The study also concluded that patients who changed therapy at the time the resistance testing was conducted experienced a 'vastly superior response compared to those who did not.' Almost 80% of patients who changed therapy at the time of resistance testing received three or four active drugs compared with just 23% of those who did not change.
"We are extremely encouraged by these results," said Neil Graham, MD, Vice President of Clinical and Medical Affairs at Tibotec-Virco. "These substantive data from clinical practice have been collected by one of the foremost HIV clinics in Europe and indicate that the benefit of resistance testing can be substantial and long-lasting."
HIV drug resistance testing background
The ability of HIV to develop mutant strains that are resistant to HIV drugs is one of the main reasons why people living with HIV experience treatment failure. Drug resistance tests help physicians select effective drugs to use in combination therapy and have, therefore, become a critical component in the clinical management of HIV infection. Historically there have been two main approaches to HIV drug resistance testing.
Phenotyping is a direct measure of resistance: 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. The susceptibility of the virus to each drug is measured and compared to a standard reference virus and the results expressed as a fold-change in resistance relative to this standard. This is highly complex and time-consuming to perform.
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. While this is quicker and easier to perform than phenotyping, the major limitation is that there are approximately 250 mutations that can interact and counteract one another in highly complex ways to cause resistance, making the interpretation of raw genotypic resistance information extremely difficult. Interpretation has traditionally been attempted using mutation tables, rules or subjective methods to predict whether a virus will be sensitive or resistant to each drug.
Virco's solution to this challenge 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 computerised system that searches the world's largest database of approximately 100,000 genotypes and phenotypes for virus 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 a quantitative estimate of resistance to each drug available. Data from a number of studies has shown that the VirtualPhenotype™ is a significant independent predictor of treatment response.
Tibotec-Virco is a multinational biotechnology company with operating subsidiaries in the United States, Belgium, the United Kingdom, and Ireland. Tibotec-Virco sells its resistance testing services under the name of Virco via Quest Diagnostics, Laboratory Corporation of America Holdings (LabCorp) and ARUP Laboratories in the USA, SRL in Japan, as well as directly to HIV/AIDS centres in Europe, Canada and Australia.
The Tibotec-Virco group was formed from the merger of Virco Group NV and Tibotec Group NV on March 14, 2001 and brings together the complementary expertise of Tibotec in drug discovery and development and that of Virco in pharmacogenomics and molecular diagnostics. Tibotec-Virco applies the latest techniques in pharmacogenomics, molecular biology, drug discovery and development, and artificial intelligence to develop individualised disease management products, services and technologies in HIV, other infectious diseases and cancer with the ultimate aim of enhancing and extending peoples' lives.
Tibotec-Virco is widely regarded as a world leader in HIV resistance testing and has developed some of the most widely available and trusted diagnostics in the world. The company has a number of genomics-based diagnostic tests under development for use in the management of hepatitis and cancer. The current focus of the company's drug discovery and development activities is the clinical development of a number of HIV/AIDS drugs that are active against strains of HIV that have developed drug resistance (a major cause of treatment failure).
For further information, please visit Tibotec-Virco's website:http://www.
U.S. Contact: Peter Vigliarolo, Cooney/Waters -- 212/886-2200
Virco: Dr. Andrew Revell, 44-(0)-1223-728830, 00-(54)-1141-669210