AIDS Prevention Vaccine May Instead Cause The Disease
Dow Jones Newswires
GENEVA (AP)--A weakened virus that many consider
the best hope for an AIDS vaccine suffered a serious
setback Thursday when tests in adult monkeys showed it
may actually cause the disease it was meant to prevent.
The approach - what scientists call a live, attenuated
vaccine - initially protects monkeys from getting infected
with the simian version of HIV.
However, the new work shows that over time, the
weakened virus can mutate into a lethal form that causes
the disease it was meant to prevent.
"To me, this fortifies that we are not ready to go into
humans with a live attenuated vaccine," said Dr. Anthony
Fauci, head of the National Institute of Allergy and
Infectious Diseases.
Dr. Robert Gallo of the University of Maryland said that
if the live attenuated approach fails, it means AIDS
vaccine development is no further ahead than it was in
1984, when little was known about the epidemic's
cause.
"We have no guarantee that we will ever have a
vaccine," he said.
Creating an AIDS vaccine is a top priority of
researchers but also an extraordinarily difficult task
because the AIDS virus attacks parts of the immune
system that are ordinarily called into action by effective
vaccines.
One idea is to give people a weakened version of HIV _
one that would set up a harmless low-grade infection but
keep immune defenses on high alert against the real
thing. People who carry genetically crippled HIV that
arose through random mutations do not seem to get sick.
Because of the obvious hazards of testing even a
weakened AIDS virus on people, scientists at the New
England Regional Primate Center in Southboro, Mass.,
created a mirror version using the closely related simian
immune deficiency virus, SIV.
When first tested on macaque monkeys, they found that
the vaccine seemed to completely protect them from
what should have been lethal doses of the full-strength
virus.
However, in 1995, Dr. Ruth Ruprecht of Dana Farber
Cancer Institute in Boston found that the weakened virus
eventually triggered the simian version of AIDS when
given to baby monkeys.
At the 12th World AIDS Conference, Ruprecht
reported her new research shows that in time, the
vaccine also causes AIDS in adult monkeys.
"What we saw in infants is a fast-forward version of
what could happen in adults with an attenuated vaccine,"
she said.
The version of the vaccine she tested was weakened by
deleting parts of three genes that were thought necessary
for it to cause illness.
Los Angeles AIDS specialist Charles Farthing, who
wants to test a live attenuated HIV vaccine in people,
called Ruprecht's latest discovery "more concerning"
than her earlier work in infants. Still, he said, monkey
AIDS is an even more virulent disease than human
AIDS, and the human vaccine would be weakened even
more than the monkey version she tested.
"Looking at SIV in monkeys gives you a misleading
impression of what would happen in human beings," he
said. "This is not safety data for humans."
Ruprecht vaccinated 15 adult monkeys over the past
three to five years. One has died of AIDS. Three others
have high levels of the HIV virus in their blood.
Among nine infant monkeys vaccinated, six have
developed AIDS and five of them are dead. The other
three have pre-AIDS abnormalities.
She said the weakened virus mutates so rapidly that
strains eventually emerge that are able to thrive.
"There is a mini-Darwinian experiment going on in every
single vaccinated animal," she said. "In the end, we have
disease." |
