First days after HIV infection may hold vaccine key

By Laura MacInnis

GENEVA (Reuters) - The body's initial response to contracting HIV could provide the answers scientists need to develop a vaccine for the AIDS-causing virus, a Nobel-winning expert said on Monday.

The AIDS epidemic has killed about 25 million people, and about 33 million worldwide are now infected with HIV. Cocktails of drugs can control the virus but so far there is no cure.

Francoise Barre-Sinoussi, who shared the 2008 Nobel prize for medicine with Luc Montagnier for their discovery of HIV a quarter-century ago, told a World AIDS Day event that the human body reacts very distinctly -- and quickly -- to HIV infection.

The nearly immediate cellular responses seen in the gut and elsewhere could point scientists towards a vaccine that keeps HIV from taking hold and morphing into the immunity-destroying disease, the French expert said.

"Everything is decided very early after exposure to the virus ... When I say very early after, it is a matter of days," she said in a speech at the World Health Organisation.

"If we know better the early events of the acute infection, we can think about developing a better vaccine strategy," she said, warning: "If we don't make progress in this basic knowledge, we will never have a vaccine."

Recent efforts to develop a vaccine by jump-starting immune-system cells that tackle the virus -- such as one last year by Merck -- have yielded disappointing results.

Experts agree that any vaccine must generate neutralising antibodies -- immune system proteins that flag and attack invaders such as viruses -- as well as so-called cell-mediated immunity, the T-cells that directly attack invaders.