Scientists announced for the first time on Thursday that they could be nearing a cure for Aids, the worst infectious disease of modern times which has already claimed 25-million lives worldwide.
A decade after the development of a therapeutic drug cocktail which went some way to transforming Aids from a killer infection to a chronic disease, doctors believe they may have made the next big breakthrough.
Aids is unique because even after treatment with a cocktail of powerful drugs, a "latent" virus remains in the body's DNA and erupts as soon as treatment stops.
The active virus is destroyed by the drug cocktail of anti-retroviral (ARV) therapy now the standard treatment for HIV. But the latent virus remains hidden and scientists had believed it was impossible to selectively kill the infected cells or to flush out the virus hidden in them.
United States scientists found that combining a cheap drug called valproic acid with the existing ARV cocktail used to treat the disease, caused the level of "latent" HIV to fall dramatically.
The scientists now believe they may be able to eliminate the latent HIV altogether, effecting a cure.
David Margolis, who led the research team at the University of North Carolina, said: "Our findings suggest that eradication of established HIV infection might be achieved in a staged approach.
"This finding, though not definitive, suggests that new approaches will allow the cure of HIV in the future."
He added: "Patients ask me all the time: 'When can I stop taking these drugs?' I would like to set scientists on the way to looking for a means to eradicate the virus. That is why I am excited about this.
"But I don't expect it to happen soon. In the meantime, prevention has to be the key message."
The US team describe their research as a "proof of concept" study which involved testing four patients who had been on longterm treatment with the standard drug cocktail.
They say it opens up new research possibilities but it will be many years before a new treatment results.
If eradication of the virus could be achieved it would mean Aids patients would be able to stop taking drugs and would cease to be infectious, halting spread of the disease.
The advance, published in The Lancet, created immediate controversy with some scientists hailing it as a breakthrough while others warned against talk of a cure. One dismissed the researchers' claims.
Jean-Pierre Routy, of McGill University in Montreal, Canada, says in the Lancet that the finding "merits further urgent study".
He said: "It is a milestone. It paves the way to a possible cure. Last week we thought it was impossible (to eradicate the virus). Now for the first time this finding shows it could be workable."
In the UK, Robin Weiss, professor of virology and an expert on HIV at University College, London, said: "This is a potentially exciting advance, but any talk of curing infection is premature."
Professor Brian Gazzard, a specialist in HIV at Chelsea and Westminster Hospital in London, said: "If true, it would be very exciting. The single most important challenge in Aids treatment is how to eliminate latent virus."
But Abraham Karpas, assistant director of research in the department of virology at the University of Cambridge, said: "It is absolute nonsense. They don't understand the biology of the virus. We will cure every cancer before we find a cure for HIV. The only way to defeat this disease so far is to prevent infection."