Bad news for HIV-vaccines?Double virus infection worries some
AIDS researchers.
28
November 2002
TOM
CLARKE
 |
| More than 40 million
people have HIV. |
| ©
GettyImages | | |
A patient with some immunity to one strain of HIV
virus has become infected with another strain1.
This could spell trouble for urgently needed HIV
vaccines, warn researchers. Others think the case has
little bearing on immunizing healthy people.
This alarming controversy has emerged on the eve of
World AIDS day, as the United Nations announces that
more than 40 million people worldwide are now infected
with the virus.
The patient had been on 'stop-start' HIV therapy.
Under this regimen, a patient takes anti-HIV drugs until
the virus is suppressed, and then they stop. When the
virus rebounds, undamaged parts of their immune system
that had recovered during treatment keep the virus in
check, often for months. As the virus gradually beats
the immune system, they start taking the drugs
again.
Several cycles into his treatment, the patient had
"an extremely vigorous response to his virus", says
Bruce Walker of Harvard Medical School in Boston,
Massachusetts, who led the study1.
The patient then caught a second, different strain of
HIV - probably from sex with another HIV-infected person
- and his immune system collapsed rapidly.
This is the first case of so-called 'superinfection'
in someone who had immunity to their initial infection2.
"We thought for a long time that if you get infected
with one strain of HIV that you are well protected from
another," says Walker.
There are countless strains of HIV. The hope has been
that a vaccination against one would lead to immunity to
the rest. The patient's second infection was caused by a
closely related strain that is common in North America.
"But it clearly was not something his immune system
could deal with," says Walker.
|
The immune response of someone
with HIV is never going to function normally
|
|
Sarah
Rowland-Jones
University of
Oxford | | |
Hopes for an effective HIV vaccine are far from
dashed, however. "It's probably not good news," says
HIV-vaccine researcher Sarah Rowland-Jones of the
University of Oxford, UK, but vaccinated healthy people
are likely to be very different. "Even at its best, the
immune response of someone with HIV is never going to
function normally," she says.
Indeed, the patient lacked cells that produce
neutralizing antibodies to help destroy pathogens. "Half
his immune system was missing," says Ruth Ruprecht, a
vaccine researcher at the Dana-Farber Cancer Institute
in Boston, Massacheusetts.
It is also possible that Walker's patient was a very
rare case. It is not known how many HIV-positive people
are exposed to other strains of the virus and fight them
off.
There is one concrete conclusion from the study, says
Anthony Fauci, director of the US National Institute of
Allergy and Infectious Diseases in Bethesda, Maryland:
"It is imperative that safer sex be practised during
each encounter, even when both partners are
HIV-infected." | 
