Scientists have captured an image of the AIDS virus in a biological handshake with the immune cells it attacks, and said today they hope this can help lead to a better vaccine against the incurable disease.
A 3-D X-ray crystallographic image showing the broadly neutralizing antibody b12 (green ribbon) in contact with a critical target (yellow) for vaccine developers on HIV-1 gp120.
They pinpointed a place on the outside of the human immunodeficiency virus that could be vulnerable to antibodies that could block it from infecting human cells.
US National Institutes of Health researcher Peter Kwong said the study, published in the journal Nature, may reveal HIV's long-sought "site of vulnerability" that can be targeted with a vaccine aimed at preventing initial infection.
"Having that site and knowing that you can make antibodies against it means that a vaccine is possible," Kwong said in a telephone interview.
"It doesn't say we've gotten there. But it's taken it off the list from an impossible dream and converted it to something that is a (mere) technical barrier."
Experts agree that a vaccine is the only hope of stopping the pandemic of AIDS, which has killed more than 25 million people since it was first recognized in 1981. About 40 million people now live with HIV, with sub-Saharan Africa hardest hit.
But while dozens of potential vaccines are in development, only two AIDS vaccine candidates are in advanced human trials -- one made by Merck and Co. and another by Sanofi-Aventis SA.
Because the virus attacks immune system cells, it has been especially difficult to design a vaccine to fight it.
The team at the National Institute of Allergy and Infectious Diseases, part of the NIH, made atomic-level images of the virus.
They revealed the structure of a protein on the surface of HIV as it looks while the protein is bound to an infection-fighting antibody. They said this protein, called gp120, seems susceptible to attack by this antibody, which is called b12 and is capable of broadly neutralizing the virus.
An antibody is an immune system protein that helps seek and destroy invaders like viruses and bacteria.
The researchers detailed the precise interaction as the virus tries to grab and infect cells sent to protect the body.
"The first contact is like a cautious handshake, which then becomes a hearty bear hug," said Dr. Gary Nabel, an NIH vaccine expert and a co-author of the research.
The virus uses the protein gp120 to gain entry into the CD4 T-cells it infects. But the researchers also found that the antibody b12 can block this process.
The virus mutates quickly and continuously to beat the immune system's efforts to target it. It also is cloaked in such a way that it stops antibodies from blocking the proteins that HIV uses to bind to a cell and infect it.
So this is a critical area of vulnerability, Nabel said. "This is certainly one of the best leads to come along in recent years," he said.
NIAID Director Dr. Anthony Fauci said the findings are of great importance, but much more work in animal and human studies is needed, and any vaccine is years away.
"I don't think there's any one particular thing that, in and of itself, is the show-stopper. But I don't think we could really make substantial, fundamentally scientifically based progress until we got this very important information," he said.