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Merck Announces Promising Monkey Data for Two AIDS Vaccines

April 02, 2001

Pharmaceutical giant Merck & Co. has announced that two of its candidate AIDS vaccines have shown promise in monkeys. Both vaccines are now in Phase I human safety testing.

When inoculated with Merck's experimental vaccines, the laboratory animals remained healthy after they were exposed to an AIDS-like virus that infects monkeys, according to data released by Merck at the AIDS Vaccines in the New Millennium conference in Keystone, Colorado, in presentations 31 March and 2 April.

Still, however, it is not clear whether the vaccines will have any effect in humans and, if they do, how well they will work or for how long. Similar to most experimental AIDS vaccines, these did not prevent infection in monkeys but rather held it in check.

"We are definitely hopeful, (but) there's a great deal of difference between testing in primates and testing in people," Dr. Emilio Emini, who heads Merck's vaccine program, told the Wall Street Journal.

Currently Merck's vaccines are being tested in phase I human trials, the first of three stages of human testing before a vaccine can be licensed. Phase I trials enroll small numbers of volunteers primarily to test safety and typically take a year to complete.

"This is exciting news, because a preventive vaccine is the world's best hope for ending the AIDS epidemic," said Dr. Seth Berkley, president of the International AIDS Vaccine Initiative. "The news is all the more exciting because it comes from the pharmaceutical industry, which until recently was reluctant to get involved with AIDS vaccines. Because most vaccine-making expertise resides in the private sector, at companies like Merck, the world will not find an AIDS vaccine unless industry is fully engaged in the hunt."

Drug maker GlaxoSmithKline announced earlier this year that it too is working on an AIDS vaccine and hopes to begin human testing by the end of the year.

Preventive AIDS vaccines are designed to prepare the immune systems of healthy people to recognize and control HIV, the virus that causes AIDS. This way, in the event of later exposure to HIV, the body can launch a swift counterattack to control the infection.

Merck's vaccines aim to stimulate cellular immune responses, an arm of the immune system that seeks out and destroys cells infected with HIV. The vaccines consist of pieces of HIV's genetic material that are able to stimulate cellular immune responses. Because only fragments of the viral genes are included, the vaccines cannot cause HIV infection.

One of the vaccines is derived from a modified version of adenovirus, which causes a form of the common cold. The other is a so-called naked DNA vaccine.