Photo illustration depicting the new human antibodies in red with green and yellow oval loops on an HIV model. The approximate location of the viral membrane is shown in blue. (Illustration by Christina Corbaci and Rob Pejchal/Science)

The discovery of two new powerful antibodies that neutralize HIV strains could help vaccine developers.

In this week's issue of the journal Science, researchers targeted what appears to be an Achilles heel of the virus after checking for antibodies in the blood of 1,800 people infected with HIV.

"The findings themselves are an exciting advance toward the goal of an effective AIDS vaccine because now we've got a new, potentially better target on HIV to focus our efforts for vaccine design," Wayne Koff, senior vice-president of research and development at the International AIDS Vaccine Initiative, which led and sponsored the study.

Researchers said these are the first broadly neutralizing antibodies to have been identified in more than a decade.

The newly identified antibodies, called PG9 and PG16, are also the first to be isolated from donors in seven sub-Saharan countries, where most new HIV infections occur.

Part of the problem in developing HIV vaccines is that the virus mutates so readily that someone may be infected with millions of different versions, and each one looks different to the immune system. Drug cocktails have helped to keep the virus under control but no drug eradicates it.

The antibodies seem to bind to a region of the virus at sites that the researchers believe are more accessible than those used by previously discovered antibodies.

"The results provide a framework for the design of new vaccine candidates for the elicitation of [broadly neutralizing antibody] responses," the study's lead researcher, Dennis Burton, of the IAVI Neutralizing Antibody Center at The Scripps Research Institute in La Jolla, Calif, and his co-authors concluded.

Better 'bait' for vaccine search

Specifically, the two antibodies target a protein that forms a spike that the virus uses to infect cells and does not change. That may explain the potency of this new approach, and its ability to tackle so many subtypes of the virus.

"If you think of it as a fishing expedition, we and the rest of the field were previously using the wrong bait in the search for HIV-specific broadly neutralizing antibodies," said Christos Petropoulos, chief scientific officer and vice-president of virology research and development at Monogram Biosciences, which helped to screen blood for the antibodies.

A minority of people with HIV produce these broadly neutralizing antibodies. It's hoped that if an HIV vaccine helps the immune system to produce the powerful antibodies before exposure to HIV then the disease could be prevented.

The next step in the research is to stimulate the development of these antibodies in animal and human studies. Even if those experiments are successful, a vaccine is years away, AIDS experts cautioned.

Scientists at the the biotechnology company Theraclone Sciences also contributed to the research by identifying the antibodies involved.

The study was supported by the International AIDS Vaccine Research Initiative, USAID and NIAID.