Agence France Presse (04.05.12) - Monday, April 09, 2012
Differing levels of antibody responses may help explain the
results of a 2009 trial in which an AIDS vaccine candidate was
shown to protect 31 percent of participants, according to a
new report.
The new analysis of those initial results indicates the IgG
antibody, created by the body to stave off infection, was able
to attach itself to the surface of the HIV protein - a region
referred to as V1V2 - and, in fact, prevent infection in some
individuals who received the vaccine versus the placebo.
However, participants demonstrating the highest levels of
another antibody, IgA, seemed more vulnerable to HIV than
those with lower levels. This led scientists to believe IgA
could have hindered the vaccine and rendered it less
effective.
"This analysis has produced some intriguing hints about what
types of human immune responses a preventive HIV vaccine may
need to induce," said Anthony Fauci, director of the National
Institute of Allergy and Infectious Diseases (NIAID).
The data were gleaned from a trial involving 16,395 HIV-
negative volunteers in Thailand; it was funded by NIAID, the
US Army Medical Research and Materiel Command, and the Bill &
Melinda Gates Foundation. Although the study was considered
ground-breaking for its 31 percent protection rate, a vaccine
must offer at least 50 percent protection to be introduced in
the marketplace.
"Different HIV vaccines may protect against HIV in different
ways," said study co-author Nelson Michael, Military HIV
Research Program director at Walter Reed Army Institute of
Research.
"More research is needed to fully understand these results,
and to determine if they can be generalized to other types of
HIV vaccines or similar vaccines tested against other regional
types of HIV or via different routes of exposure," Michael
added.
The article, "Immune-Correlates Analysis of an HIV-1 Vaccine
Efficacy Trial," was published in the New England Journal of
Medicine (2012;366:1275-1286).