By
Suzanne Leigh, Medical Tribune News Service
A
new study on monkeys suggests that scientists might be gaining
ground in the long battle to develop an AIDS vaccine.
The
race to create the first AIDS vaccine lost momentum in the late
1980s, when scientists realized that methods used to make a DNA
vaccine against hepatitis B could not be replicated in a vaccine
against human immunodeficiency virus, since the HIV virus is much
more complex.
To
make a DNA vaccine, the genetic material is taken from cells infected
with a virus and injected into the body like a regular vaccine.
This vaccine then causes the body to produce a protein that triggers
the formation of killer T-cells, powerful immune-system cells
that destroy infectious agents and infected cells.
Now a study published Tuesday in the May issue of Nature Medicine
reports that a new DNA vaccine developed from harmless components
of simian, or monkey immunodeficiency virus (SIV) and HIV, may
represent a turning point in AIDS immunization.
Harriet
L. Robinson from the Yerkes Regional Primate Research Center in
Atlanta and colleagues developed a vaccination using HIV and SIV
genes. The researchers used 32 rhesus macaques, injecting half
with a vaccination using HIV and SIV genes. Forty-six and 66 weeks
later the animals were given booster immunizations with the same
genes along with a pox virus to elicit a stronger immune response.
Once in the cells, the virus did not replicate, thus posing no
risk after vaccination.
During the study, the monkeys received three ``challenges'' in
which they were exposed to both SIV and HIV. Robinson found that
viral loads remained undetectable in the vaccinated animals. In
contrast, unvaccinated macaques had high levels of the virus in
their blood.
The
study follows a similar experiment in Australia where DNA vaccines
and boosters were administered to four macaques prior to infection
with the immunodeficiency virus. The macaques produced a large
number of killer T-cells that cleared the virus from their system
within weeks. Four other macaques, which had not been vaccinated,
were found to have the virus in their blood.
However,
significantly less virulent forms of the virus were used during
the challenge phase of the Australian study, compared with the
U.S. trial.
According
to Dr. Margaret Liu, vice president of vaccine research at Chiron
in Emeryville, Calif., a pharmaceutical company that is researching
another DNA-based AIDS vaccine, the initial findings of the Robinson
study are promising.
``We're
seeing a number of studies in the field of vaccine development
that are making us feel very hopeful and this study is in keeping
with that,'' she said.
Liu
said she believes that no single study will represent a breakthrough
and that the eventual AIDS vaccine will be a culmination of advances.
As for when she would expect an AIDS vaccine to be available,
Liu refuses to speculate.
``We're
pedaling as fast as we can and I can say that I'm confident we're
getting closer,'' she said.
But
for some AIDS advocates, the Robinson study, like others before
it, emphasizes the need for vaccine research to go beyond animal
studies.
``This
is yet another example of tantalizing results of the potential
of HIV vaccines to protect people,'' said Sam Avrett, executive
director of the Washington, D.C.-based Aids Vaccine Advocacy Coalition.
``Data
like this underscores the need for a faster pace of research and
stronger product development to bring the best vaccine concepts
into human trials,'' he said.
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