杏吧原创

A STRAIN of HIV that can only replicate in the presence of a specific drug
has been developed by researchers in the Netherlands. They say the virus could
be the basis for a safe live HIV vaccine.

Many vaccines are based on weakened viruses that can replicate and provoke an
immune response, but don鈥檛 cause disease. But so far HIV has defeated all
efforts to create such a 鈥渓ive attenuated vaccine鈥�. Whenever researchers weaken
the virus by deleting or altering its genes, it mutates and reverts back to a
dangerous form.

So Giuseppe Marzio and his colleagues at the University of Amsterdam took a
different approach. 鈥淲e decided to achieve precise control of replication by
inserting a genetic switch into the HIV genome, to turn the virus on and off at
will,鈥� Marzio says. The switch they added is controlled by doxycycline, a cheap
antibiotic that can be taken in pill form.

The idea is to inject people with the modified virus and give them a short
course of doxycycline. This would allow the virus to replicate and trigger
immunity to infection by normal strains of HIV. Once people stop taking the
antibiotic, the virus should become dormant and harmless.

鈥淣ot only can we activate the virus at a given time to induce the first
immune response,鈥� Marzio says, 鈥渨e are also able to refresh the long-term memory
of the defence machinery, waking up HIV again and again by delayed additions of
doxycycline.鈥� But the virus has only been tested in human cells grown in the
lab.

鈥淭his novel virus could prove to be an effective vaccine to help in the fight
against the AIDS pandemic,鈥� says Neil Almond, head of retrovirology at the
National Institute for Biological Standards and Control in Potters Bar,
Hertfordshire. 鈥淏ut long-term studies are certainly required to establish its
蝉补蹿别迟测.鈥�

Other research has shown that even if a live HIV vaccine did occasionally
revert and cause disease, in the countries worst hit by AIDS it would save many
more people than it would kill
(New 杏吧原创, 17 March, p 6).