antibody vaccine to HIV

antibody vaccine to HIV - news feature Back to plan A The...

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F ew clinical-trial results have had as much riding on them as those ann- ounced in February by a small biotech firm called VaxGen. The company, based in Brisbane, California, was the first to push a vaccine against HIV into ‘phase III’ clinical trials — the final tests that help regulators decide whether a drug should be put on the market. If the vaccine had worked, it would have been a watershed in worldwide efforts to defeat a disease that kills some 3 million people each year. But when the numbers came in, they told a disappointing story. VaxGen gave its product, called AIDSVAX, to 3,330 high-risk volunteers — mostly homosexual men — from North America and Europe. Of those people, 5.7% contracted HIV, compared with 5.8% of the 1,679 volunteers who did not receive the vaccine. Despite efforts by VaxGen to argue that AIDSVAX performed better in certain ethnic groups, it was clear that the vaccine was a bust. For many AIDS researchers , the vaccine’s failure wasn’t too surprising. VaxGen’s charismatic co-founder, Don Francis, had raised the money to go ahead with phase III trials after the US National Institute of Allergy and Infectious Diseases (NIAID) decided not to bankroll the project. AIDSVAX consists of a protein called gp120, a major component of HIV’s outer coat. It is designed to stimulate the production of antibodies that will prevent the virus from locking onto the immune cells that it infects, called helper T cells. Yet despite promising results from an early study in chimpanzees 1 , most of the human data on gp120 were extremely discouraging. In particular, antibodies taken from people immunized with the protein showed little ability in lab tests to prevent HIV from infecting its cellular victims 2 . Given these results, most AIDS vaccine researchers long ago gave up on the idea of stopping HIV in its tracks by stimulating the production of antibodies. Instead, they began to design a second generation of AIDS vaccines that would spur the body to make armies of killer T cells — the foot soldiers of our cellular immune response. Whereas antibodies can in theory lock onto viruses in the bloodstream and prevent them from infecting their target cells, killer T cells search out and destroy those host cells that have been infiltrated by a viral invader. Many of these second-generation vac- cines are now working their way through clinical trials. But for the most part, they show no signs of being able to halt HIV com- pletely. “People are increasingly realizing that they’re not going to be able to do it all with cellular immunity,” says Dennis Burton, an immunologist at the Scripps Research Institute in La Jolla, California. So antibodies are coming back into fash-
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antibody vaccine to HIV - news feature Back to plan A The...

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