Gilead and Virco Announce U.S. Collaboration to Promote One of the First Pharmacogenomic Applications for HIV Resistance Tests and Services

New Phenotypic and Genotypic Tools for U.S. Physicians in HIV Disease Management

Foster City CA and Baltimore, MD -- March 7, 2000

Gilead Sciences, Inc. (Nasdaq: GILD) and Virco today announced a collaboration to promote Virco’s HIV resistance monitoring tests and services (Antivirogram,™ VircoGEN™ and VirtualPhenotype™) designed to characterize the susceptibility to available drugs of the human immunodeficiency virus (HIV), the virus that causes AIDS. HIV mutations can arise quickly and result in resistance to drugs used to treat the deadly infection. Virco’s phenotypic and genotypic services as well as its extensive database of HIV genome sequences and corresponding measures of virus susceptibility help physicians identify resistance mutations, interpret results and better determine which combination of anti-HIV drugs will most effectively inhibit HIV replication on an individual patient basis.

The Virco phenotypic and genotypic services are currently offered through Laboratory Corporation of America® Holdings (LabCorp®; NYSE: LH), a national clinical laboratory with a premier HIV testing facility in Research Triangle Park, North Carolina. For more information, please visit http://www.gilead.com/wt/off_site?offsite=www.labcorp.com

Under the terms of the agreement, which becomes effective on April 1, 2000, Gilead will promote the Virco portfolio of phenotypic and genotypic tests and interpretive services to HIV treating physicians in the United States. Gilead has developed relationships with a significant number of HIV treaters nationwide as a result of marketing VISTIDE® (cidofovir injection) for CMV retinitis in AIDS patients and its clinical development programs for nucleotide antiretrovirals used to treat HIV infection. The companies will work together to develop educational and promotional campaigns. Gilead and Virco anticipate extending this collaboration to Europe and Australia in the coming months.

“We are very pleased to be working with Gilead. The company’s sales representatives are experts in the HIV treatment area and are particularly familiar with the issues of viral resistance,” said Paul Stoffels, M.D., President and Chief Executive Officer of Virco. “As with any new technology, the education process is a critical aspect of market development, and the Gilead team is well established in this role. They are ideally suited to help us bring these important diagnostic tools to the physicians and patients who most need them.”

Data presented this year by Virco scientists at the 7th Conference on Retroviruses and Opportunistic Infections demonstrated that phenotypic testing significantly improves virologic response for patients on anti-HIV therapy, indicating that such testing can better help physicians select optimal treatment regimens. This was the first major prospective study to show the benefit of HIV phenotypic drug susceptibility testing compared to the traditional approach of using medical history to construct a new anti-HIV drug regimen for patients who have failed therapy.

Drug resistance has emerged as a critical treatment issue because it threatens to erode the significant progress that has been achieved in the fight against HIV infection. Combination regimens of three or more potent anti-HIV drugs have helped many patients infected with HIV live longer, healthier lives. However, initial treatment success can be difficult to maintain. Of the nearly 350,000 patients currently receiving anti-HIV treatment in the United States, an estimated 60 percent are failing their current treatment, in part due to the development of drug resistance caused by viral mutations.

“One of the biggest challenges physicians face today is choosing effective new anti-HIV drug regimens for patients who have developed resistant viral strains and have begun to fail therapy,” said John Mellors, M.D., from the University of Pittsburgh Medical Center. “With the proper guidance, phenotypic and genotypic tests are important tools to help physicians develop individualized strategies designed to minimize the emergence of HIV resistance and maintain suppression of HIV.”

As part of the collaboration, Gilead’s sales force will conduct an intensive educational campaign to help inform physicians about the pharmacogenomic approach to disease management for their patients with HIV infection. Specifically, physicians use analyses of a patient’s HIV genome – in this case, using phenotypic and genotypic tests – to strategically select a drug treatment regimen that will deliver the most potent antiviral attack on the patient’s unique HIV strain. The prescriber relationships built and maintained during the term of this agreement will also enhance Gilead’s ability to develop and later commercialize new therapies for HIV infection.

“We have been working closely with Virco for several years now, conducting extensive phenotypic and genotypic testing to better understand the resistance profiles of our investigational drugs and how they might work in combination with other antiretroviral agents,” said John C. Martin, Ph.D., President and Chief Executive Officer of Gilead Sciences. “This new collaboration with Virco underscores our belief that these pharmacogenomic tools may offer significant benefits in selecting antiretroviral therapies for many patients and will become more broadly used as physicians gain experience with these services.”

Gilead sales representatives will promote the following Virco resistance tests and services:

Antivirogram Phenotypic Resistance Test. The Antivirogram directly assesses the susceptibility of an HIV strain to each antiretroviral drug currently available for use in combination anti-HIV drug regimens. A sample of a patient’s HIV viral population (by recombinant phenotype) is tested in the presence of each drug and the ability to inhibit viral replication is measured. The Antivirogram determines the combined effect of all HIV mutations present and their possible interactions, including the effect of genetic changes as yet unknown or not previously identified. This test is useful for patients who have failed previous therapies or when new drugs are available for which the mutational pattern is not yet known.

VircoGEN Genotypic Resistance Test. The VircoGEN test evaluates the probability of viral resistance by analyzing a segment of a patient’s HIV genome to identify mutations that have been linked to resistance and/or cross-resistance to antiretroviral agents in previous studies. This test cannot detect unrecognized genetic mutations or interactions between mutations that may affect drug susceptibility. VircoGEN can be most useful before treatment begins or in the early stages of therapy when a patient’s HIV has not been subjected to the pressure of many different anti-HIV drugs, and there are fewer mutations in the viral genome. It is also more rapid and less expensive than phenotypic resistance testing.

VirtualPhenotype Genotypic Interpretation. VirtualPhenotype is an interpretive service based on an extensive correlative database of more than 12,000 HIV phenotypes and genotypes, the world’s largest database of its kind. The aim of this service is to offer the best genotypic interpretation possible based on real data (Antivirogram and VircoGEN results) recorded in Virco’s correlative database. VirtualPhenotype is also available to physicians who use other phenotypic and genotypic products. When combined with expert physician judgment and a patient’s treatment history, VirtualPhenotype will help physicians use genotypic information optimally.

“We are excited about the additional promotional and educational support that Gilead will provide HIV clinicians and their patients to help increase awareness of the need for resistance testing,” said Myla P. Lai-Goldman, M.D., Executive Vice President, Chief Scientific Officer and Medical Director of LabCorp. “HIV resistance testing has recently received support from the Department of Health and Human Services’ Panel on Clinical Practices for treatment of HIV infection for use in clinical practice. We anticipate that phenotypic and genotypic testing will increase over the coming months.”

About Gilead and Virco

Gilead Sciences, headquartered in Foster City, CA, is an independent biopharmaceutical company that seeks to provide accelerated solutions for patients and the people who care for them. Gilead discovers, develops, manufactures and commercializes proprietary therapeutics for challenging infectious diseases (viral, fungal and bacterial infections) and cancer. Gilead maintains research, development or manufacturing facilities in Foster City, CA; Boulder, CO; San Dimas, CA; Cambridge, UK and Dublin, Ireland and sales and marketing organizations in the United States, Europe and Australia.

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 believes it provides the most sophisticated and comprehensive portfolio of phenotyping and genotyping decision support tools for HIV physicians. Antivirogram is currently available in the United States via Laboratory Corporation of American Holdings (LabCorp). Virco also sells its testing services to several major European AIDS centers as well as in Canada, Japan and Australia. For further information, please visit http://www.gilead.com/wt/off_site?offsite=www.vircolab.com.