(Adds background on other HIV vaccines, paragraphs 8, 9) By Laura MacInnis GENEVA, Dec 1 (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. About 30 different vaccines are now in various stages of testing. Barre-Sinoussi said "conventional" vaccines would not be enough to tackle HIV, which is a retrovirus, which like all viruses copies its genetic code into the DNA of its host but uses RNA -- a working form of DNA -- instead of DNA to do so. "We have to consider the conventional approach together with another approach that considers the pathogenic signals," she said. "We need to understand better the role of genetics." The Institut Pasteur expert also called for more research into co-infections between HIV and tuberculosis, and hit back at those who say the billions of dollars that have been funnelled into AIDS projects have drained funds needed for other diseases. "I am a little bit surprised to see an opposition between the fight against HIV and other primary health issues. It is a total misunderstanding and a major mistake," she said. "I do not understand why these people cannot work together." (Editing by Katie Nguyen)
People suffering from HIV/AIDS gather at a counseling centre during an AIDS awareness rally to mark the World AIDS Day in the northeastern Indian city of Siliguri December 1, 2008. HIV/AIDS ...
