Important note: Information in this article was accurate in 2006. The state of the art may have changed since the publication date.
USIS Washington File - June 12, 2006
Finding a vaccine against HIV has become the most difficult scientific problem in the 25-year history of the epidemic, experts say.
Medical science is able to make a vaccine work by finding a way properly to trigger the immune system to mount a response to an invader. But HIV is a virus that so successfully disables the human immune system, researchers are thwarted in their work.
This new research found that monkeys vaccinated against simian immunodeficiency virus (SIV) survived longer after deliberate SIV infection than animals not vaccinated.
SIV is a close relative of the HIV virus that plagues almost 40 million people around the world and causes an animal disease similar to that found in humans.
Two teams of researchers set out to test the theory that an imperfect HIV vaccine still might allow infected individuals to live longer and healthier lives, even while it failed to give them immunity.
Dr. Normal Levin led a team from Beth Israel Deaconess Medical Center at Harvard Medical School and the National Institute of Allergy and Infectious Diseases (NIAID)'s Vaccine Research Center (VRC). Mario Roederer of the VRC led a second team.
Watching the behavior of a special subset of immune cells after a vaccinated monkey is infected was key to determining whether a survival advantage could be gained from an imperfect vaccine, according to a June 9 NIAID press release.
These special cells are known as memory CD4+ T cells and are critical to the immune system's ability to muster an immune response.
Normally, a rapid, significant loss of these memory CD4+ T cells occurs very early, only about 10 days into an SIV infection, when levels of virus in the bloodstream are at their peak.
Up to 80 percent of memory CD4+ T cells in some tissues become infected and are lost, significantly damaging the immune system.
In this research, the vaccinated monkeys had a significantly different reaction after infection. Three times to five times fewer memory cells in the vaccinated group were infected and destroyed.
"If the virus wipes out only a fraction of the memory CD4+ T cells that it might otherwise destroy, that should allow [the animals] to live longer," said NIAID's Roederer.
The research teams found that the levels of CD+4 T cells remained at significantly higher levels in the vaccinated animals for the 850 days they were studied.
"Although our ultimate goal is to have a vaccine that completely blocks HIV infection," said NIAID Director Anthony S. Fauci, "this research suggests a potential benefit of even a partially effective vaccine."
The SIV vaccine used in this research was a simplified version of a preventive HIV vaccine developed by VRC scientists and currently is undergoing human trials for efficacy in the United States, the Caribbean and sub-Saharan Africa.
Large-scale human clinical trials are likely to begin sometime in 2007.
The full text of the press release is available at the National Institutes of Health Web site.
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