U.S. scientists have tested a new approach to AIDS therapy that raises hope of an eventual cure of the disease.  Doctors have found an old drug used for another condition can dramatically decrease the levels of the AIDS virus in the body.

HIV is a tenacious virus. Current drugs can suppress it to almost immeasurable levels to keep patients alive. But this is not a cure, since the organism continues to exist within some of the body's immune cells, although in a latent, non-replicating state. Patients must take the drugs for life to prevent this store of virus from reawakening.

Now, U.S. government and university researchers report finding a way to reduce this low level of dormant HIV much further.

Led by University of Texas scientists, they gave four patients who were already taking combinations of standard AIDS drugs an additional compound. It is valproic acid, a medication long established to prevent convulsions. The four patients took valproic acid by mouth twice daily for 16 to 18 weeks. The researchers found a 75 percent drop in the number of the dormant HIV cells in three of them.  When the treatment ended, the number of cells rebounded to earlier levels.

At McGill University in Montreal, Canada, AIDS researcher Jean-Pierre Routy, who was not involved in this study, says it is too early to talk of a cure for HIV, but he calls the results promising for their potential to deplete latent HIV reservoirs in the body.

"We can start to attack the virus where it is hiding," he said.  "We can hope one day that we can kill it or remove it from the body or kill the cells infected by the virus. So, yes, it's a glimpse of hope for sure."

The researchers present their findings in this week's edition of the medical journal Lancet.  They write that while the results are not definitive, they suggest that new approaches will allow the cure of HIV in the future.

But other scientists are cautious about the findings. Johns Hopkins University physician John Siliciano, who helped discover dormant HIV cells in the 1990s, told the Associated Press that to be useful, a drug has to kill virtually all of the cells, not merely 75 percent of them.

Rockefeller University AIDS researcher David Ho calls the finding a step forward, but a modest one. He told an NBC television Today Show interviewer that the ways of measuring HIV in this test are not precise, so the drop could be less than 75 percent.

"It [the virus] is extremely difficult to get rid of, so scientists do not want to raise false hope," said Mr. Ho.  "It's a very interesting observation, but we have to be cautious to see if this observation could be confirmed."

The researchers who reported the study say they are experimenting on larger groups of HIV patients. They say that, if their findings are substantiated, eliminating the virus in a person could occur in stages, beginning with standard combination therapy to suppress it, followed by drugs like valproic acid to complete the job.