http://news.yahoo.com/s/ap/20070921/ap_on_he_me/aids_vaccine_fails

-------------------------------------------------------------------------------

Merck's experimental AIDS vaccine fails By LINDA A. JOHNSON, AP
Business Writer
41 minutes ago

TRENTON, N.J. - A promising experimental vaccine to prevent the AIDS
virus has failed in a crucial experiment, with volunteers becoming
infected with HIV anyway, leading the drug developer to halt the
study.

ADVERTISEMENT

Merck & Co. said Friday that it is ending enrollment and vaccination
of volunteers participating in the international study, which is
partly funded by the National Institutes of Health.

Officials at Merck told The Associated Press that 24 of 741 volunteers
who got the vaccine in one segment of the trial later become infected
with HIV, the virus that causes AIDS. In a comparison group of
volunteers who got dummy shots, 21 of 762 participants also became
infected with HIV.

"It's very disappointing news," said Keith Gottesdiener, head of
Merck's clinical infectious disease and vaccine research group. "A
major effort to develop a vaccine for HIV really did not deliver on
the promise."

The study volunteers were all free of HIV at the start of the
experiment. But they were at high risk for getting HIV: most were
homosexual men or female sex workers. They were all repeatedly
counseled about how to reduce their risk of HIV infections, including
use of condoms, according to Merck.

In a statement, the NIH said a data safety monitoring board, reviewing
interim results, found the vaccine cannot be shown to prevent HIV
infection or limit severity of the disease "in those who become
infected with HIV as a result of their own behaviors that exposed them
to the virus."

The Merck vaccine was the first major test of a new strategy to
prevent HIV infection. The first wave of attempts to develop a vaccine
tried to stimulate antibodies against the virus, but that didn't work.

The new effort - and one being tried in most other current research -
is aimed at making the body produce more of a crucial immune cell
called killer T-cells. The goal is to simultaneously "train" those
cells, like an army, to quickly recognize and destroy the AIDS virus
when it enters cells in the bloodstream.

Merck and the HIV Vaccine Trials Network, an international
collaboration of researchers and institutions, co-sponsored the study.
The Merck vaccine was the farthest along of several in development,
and this was the first large-scale test of it.

The experiment, called STEP, began in December 2004 and had enrolled
3,000 volunteers in Australia, Brazil, Canada, the Dominican Republic,
Haiti, Jamaica, Peru, Puerto Rico and the United States. It aimed to
determine if the vaccine - a shot made from a weakened cold virus that
included bits of three HIV genes - could prevent HIV infection, or
reduce the amount of HIV in the blood of infected people, or both.

___

On the Net: http://www.merck.com