WASHINGTON -- Scientists have unraveled the structure of an antibody that effectively neutralizes the HIV virus which causes AIDS, the key to a possible vaccine against the fatal acquired immune deficiency syndrome, according to a report released Thursday.

"What we found was an unusual configuration of the antibody in which its two Fab domains -- the antigen recognition units -- are 'interdigitating' with each other," Scripps Research Institute Professor Ian Wilson wrote in the latest issue of the journal Science.

"Nothing like this has ever been seen before," said Wilson, one of the two Scripps professors who led the research.

"This new structure is an important step toward the goal of designing an effective vaccine against HIV, and it gives researchers a new way to design antibodies in general," said the article.

"It may enable us to make antibodies that recognize whole new sets of molecules," wrote Scripps Professor Dennis Burton, the other leader of the research.

In the same issue of Science, 24 internationally known health and research personaties called for a redoubling of efforts to find a a vaccine against AIDS, which is projected to kill some 70 million people by 2020.

"Since the discovery of HIV 20 years ago and the demonstration that HIV is the cause of AIDS, the world has awaited the development of an effective preventive vaccine," they wrote. "Almost everyone involved in HIV vaccine development agrees that there is an urgent need to create and to evaluate systematically more candidate vaccines .... The pace ... needs to be accelerated."

The Scripps team explained that HIV causes AIDS "by binding to, entering and ultimately killing "T" helper cells, immune cells that are necessary to fight off infections by common bacteria and other pathogens. "As HIV depletes the body of T helper cells, common pathogens can become potentially lethal."

The World Health Organization (WHO) estimates that around 40 million people are living with HIV worldwide, the article noted.

"During 2001 alone, more than four million men, woman and children succumbed to the disease, and by the end of that year, the disease had made orphans of 14 million children," it said. "In the United States alone, 40,000 people are infected with HIV each year."