BARCELONA, Spain, July 11 —
After
years of setbacks and even outright failure, a trickle of promising reports
offer hope that the tide may be turning in the search for a vaccine to
prevent AIDS — widely considered the most effective way to stop the pandemic
that last year killed 3 million people worldwide.
AS THE 14th International AIDS
Conference neared a close Thursday, even the most optimistic scientists
acknowledged that an effective vaccine is still years away. But, they said,
new findings and initiatives should speed up the discovery of an
immunization approach that thwarts infection.
“The pendulum has swung,” said Dr. Seth Berkley, head of the New
York-based International AIDS Vaccine Initiative (IAVI). “We think we know
what we need to do to maximize chances of success.”
Yet even Berkley, whose unbridled enthusiasm for developing an
effective vaccine that is accessible worldwide is inspiring, quickly
injected an admonition. “We won’t know for sure until we complete human
tests,” he qualified. “We think we know what we have to do. But it’s a
suspicion.”
His guarded optimism is a responsible tack in light of past failures.
Early hopes of creating a vaccine that would prevent infection with HIV were
dashed in animal studies when several such approaches produced the very
disease they were supposed to protect against.
LESSONS LEARNED
One reason scientists now believe many early strategies failed is
that they were targeting the wrong thing — or more precisely, only part of
what is necessary.
The idea behind a vaccine is simple: giving a particular virus or
bacteria to a person allows the body’s immune system to build up defenses
against it. But past that, no one really knows how any vaccines — flu, polio
or whooping cough, for example — work, said IAVI geneticist Patricia Kahn.
The body’s immune response has two distinct arms: antibodies that
seek out and destroy the virus itself and killer T-cells that raze down
cells that are already infected. Common sense would hold that annihilating
the invading virus before it ever infects cells would do the trick.
“We started out going after the antibody response,” Berkley said,
figuring that if HIV couldn’t take hold in the body, one wouldn’t fall ill.
As it turned out, “we couldn’t get enough of the right kind of
antibodies, or enough types of antibodies,” to kill the rapidly mutating
virus off, Kahn said. Even when large armies of antibodies were deployed,
some HIV slipped through.
TARGETING KILLER T-CELLS
About that time, a study of Kenyan prostitutes who seemingly had
natural immunity to AIDS — having no signs or symptoms of disease even
though they had been harboring HIV in their bodies for a decade or more —
took the scientific community by surprise. The women showed no evidence of
having mounted an antibody response to the disease, but rather, one of
killer T-cells — the second arm of the immune system.
And so the vaccine hunters
changed tactics, developing vaccines designed to stimulate the killer
T-cells to destroy cells already polluted with the AIDS virus.
Unfortunately, some of the prostitutes eventually fell ill. Again,
efforts to completely prevent HIV infection again failed.
But there was an upside: Such vaccines appeared to keep the virus in
check, preventing people infected with HIV from getting sick and dying of
AIDS. Doctors refer to the approach as a treatment, or therapeutic, vaccine.
Berkley said treatment vaccines could play an important role in
controlling the epidemic. “You could take someone who is sick, give him
anti-AIDS drugs, knocking the virus way down,” he said. “Then if you give
the vaccine, hopefully when you take the drugs away, the immune system would
keep the virus in check.”
That of course means a shorter course of drug therapy, making it more
affordable in the developing world, and less toxic to all patients.
Further, Berkley said, most scientists now believe they know what it
will take to develop an effective preventive vaccine. “The key,” he said,
“is a vaccine that stimulates both arms of the immune system” — the killer
T-cells and the antibodies.
MAJOR TRIAL ANNOUNCED
A trial of one such combination
approach is already set to get underway this year in Thailand, Dr. Anthony
Fauci, chief of the U.S. National Institute of Allergy and Infectious
Disease, announced at the conference.
The five-year study enrolling 16,000 volunteers — making it the
world’s largest HIV vaccine trial — will be conducted by the U.S.
government.
The one-two punch utilizes a canarypox virus with HIV genes inserted
to induce the destruction of already infected cells, followed by VaxGen’s
genetically engineered booster vaccine, which prevents HIV from attaching to
cells.
Based on early studies, Prayura Kunasol of the Thailand Ministry of
Public Health said she thought the combination vaccine will help about half
of those who use it.
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Meanwhile,
Berkley said, both IAVI and Merck are proceeding on other fronts. Both have
candidate vaccines that safely mounted a killer T-cell response in very
preliminary human trials. The large-scale effectiveness trials needed to
bring the IAVI vaccine to market could begin as early as 2004, he added.
The need for a preventive vaccine has never been greater, experts
here agreed, with 600 new people infected very hour.
“HIV vaccine development is not a sprint,” cautioned Dr. Lawrence
Corey, of the HIV Vaccine Trials Network. “HIV vaccines need to be developed
within the context of a larger prevention effort.”
Charlene Laino is MSNBC’s executive health editor.
ALL INFORMATION, DATA, AND
MATERIAL CONTAINED, PRESENTED, OR PROVIDED HERE IS FOR GENERAL INFORMATION
PURPOSES ONLY AND IS NOT TO BE CONSTRUED AS REFLECTING THE KNOWLEDGE OR OPINIONS
OF THE PUBLISHER, AND IS NOT TO BE CONSTRUED OR INTENDED AS PROVIDING MEDICAL OR
LEGAL ADVICE. THE DECISION WHETHER OR NOT TO VACCINATE IS AN IMPORTANT AND
COMPLEX ISSUE AND SHOULD BE MADE BY YOU, AND YOU ALONE, IN CONSULTATION WITH
YOUR HEALTH CARE PROVIDER.
"A foolish faith in authority is the worst enemy of truth."
-- Albert Einstein, letter to a friend, 1901
"I know of no safe depository of the ultimate powers of the society but the people themselves, and if we think them not enlightened enough to exercise control with a wholesome discretion, the remedy is not to take it from them, but to inform their discretion by education."
-- Thomas Jefferson, letter to William C. Jarvis, September 28, 1820
"What's the point of vaccination if it doesn't protect you from the unvaccinated?"
-- Sandy Gottstein
"Who gets to decide what the greater good is and how many will be sacrificed to it?"
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