April 9, 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).