vaccine. The monkey developed Aids and died.
Barouch and Letvin said they were not discouraged by what happened to
'Monkey 798'. They said: "[in this trial] the cup is seven-eighths
full." Certainly, several years ago this rate of success was unheard
of, and at the same time as the Harvard study, another vaccine being developed
by Merck, which wraps HIV genes inside the shell of the common cold virus,
kept monkeys' HIV viral loads undetectable for more than 500 days.
But it is a reminder that the road to an effective human HIV vaccine is
still a long one, and may take some unexpected turns. Dr Seth Berkley,
director of the International Aids Vaccine Initiative, said of the Harvard
study: "The world's scientists remain in agreement that a vaccine
for Aids is possible - just unlikely to be a home run on the next few
tries."
The Harvard vaccine was a relatively simple one made from one part of
HIV. It stimulated only one of the monkey's immune defenses - the CD8
'killer' T-cells that knock out other cells infected with HIV. But vaccines
made from other parts of HIV are needed to stimulate antibodies, which
target the virus floating free in body fluids. It is becoming clearer
that HIV's astonishing ability to outsmart simple remedies will require
a 'combination vaccine' just as much as it requires combination therapy.
A truly effective vaccine will probably contain many different fragments
of HIV, stimulating such a variety of immune responses that the virus
will be unable to escape them.
In the meantime, two authors have criticised inter-agency rivalry and
lack of political
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will, for slowing down vaccine research. US researcher John P Moore,
