After almost two decades, scientists have found a new clue that may lead to the HIV Holy Grail of a vaccine.

Scientists said on Wednesday they have found a key clue to how HIV mutates to evade the immune system that could advance the search for new drugs and a vaccine.

Researchers at the Children's Hospital Boston and Harvard Medical School in the United States have shown that the virus, which has infected 40 million people worldwide, alters its shape and triggers changes that allow it to enter cells.

They obtained a three-dimensional image of a protein called gp120, part of HIV's outer membrane or envelope, before it transforms and binds to so-called CD4 receptors on the cells it wants to infect.

"Knowing how gp120 changes shape is a new route to inhibiting HIV - by using compounds that inhibit the shape change," Stephen Harrison, head of the research team, said.

Peter Kwong, of the National Institutes of Health in Maryland, described the research as a "technical tour de force" because scientists have sought the structure of the gp120 protein before it binds to CD4 receptors for almost 20 years.

"In terms of vaccine design, the structure... reveals the envelope at its potentially most vulnerable," he said in a commentary.

HIV and AIDS have certainly had an impact on China, where the government estimates there are about 840,000 people infected.

"I think China... now has to take AIDS on as a China-wide challenge," UNICEF Executive Director Carol Bellamy said in Beijing yesterday to a forum dedicated to "A Decade of Achievement for Children."

The effects of the illness have been felt around the globe and Bellamy said the most serious challenge for children worldwide was HIV/AIDS "and the many terrible ways that is has re-defined childhood."

"I sincerely believe that most people do not really comprehend just how many young lives have been transformed for the worse by HIV/AIDS, and how many millions more are under threat," she said.

"HIV/AIDS has re-defined childhood illness; it has re-defined child labor; it has re-defined sexual abuse; it has re-defined family. Indeed it has re-defined the nature of hope itself, and it is marching onward from Africa to Russia, India, and even to China," said Bellamy.

Most efforts to help people already infected have focused on antiretroviral drugs which can prolong the lives of sufferers but are expensive and beyond the reach of millions of people.

A vaccine is considered the Holy Grail in the battle against the AIDS epidemic but efforts to find one have been hampered by HIV's ability to mutate.

"The findings also will help us understand why it's so hard to make an HIV vaccine, and will help us start strategizing about new approaches to vaccine development," Harrison explained in a statement.

The new findings published in the science journal Nature provide information about how the molecule rearranges itself before it attacks.

(China Daily/Agencies February 25, 2005)