Nature (01.04.12) - Thursday, January 05, 2012
A trial of an experimental vaccine in rhesus monkeys found it
significantly reduced their risk of infection by simian
immunodeficiency virus, which is related to HIV. Some of the
immune responses for the SIV vaccine were the same observed in
the only HIV vaccine trial in humans to have shown even
partial protection against HIV infection.
Lead study author Dan Barouch, a virologist with Beth Israel
Deaconess Medical Center in Boston, and colleagues treated
groups of rhesus monkeys with several different two-stage
vaccines: a prime vaccine composed of a virus genetically
altered to contain SIV genes, followed half a year later with
a booster made up of another virus expressing the same genes.
Six months later, the team began exposing the monkeys to an
SIV strain different from the vaccine strain, and against
which monkeys have trouble mounting a strong immune response.
The team continued exposing the animals at one-week intervals,
and most vaccinated monkeys eventually contracted SIV.
The best at preventing infection was a vaccine consisting of a
prime using modified adenovirus, and a booster using modified
poxvirus. Three-quarters of non-vaccinated monkeys developed
SIV infection after just one exposure, compared with 12
percent of those that received the best vaccine. The
researchers calculated this vaccine reduced a monkey's chance
of contracting SIV after a single exposure by more than 80
Animals that produced high levels of antibodies that attach to
the envelope protein that surrounds the virus were the most
protected against SIV. Different immune responses against the
envelope and the SIV protein called "Gag" were found in
infected animals that kept viral levels low.
The study, "Vaccine Protection Against Acquisition of
Neutralization-Resistant SIV Challenges in Rhesus Monkeys,"
was published ahead of the print edition of Nature