- GENEVA -- 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.
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- 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.
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- "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."
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- 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."
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