* Activating hidden virus means it could be detected
* Scientists say finding is significant step in AIDS fight
* Next step to study Celgene drug with experimental vaccine
By Kate Kelland
LONDON, July 22 (Reuters) - An anti-cancer drug made by the U.S. biotech firm Celgene can re-activate hidden HIV in patients so that it can be detected, bringing researchers closer to being able to treat it, Danish scientists said on Tuesday.
In a small study presented at an international AIDS conference in Australia, the researchers said the finding was a "step in the right direction" towards finding a cure for the viral disease but that many years of research are still needed.
"There is still a long way to go and many obstacles to overcome before we can start talking about a cure against HIV," said Ole Schmeltz Sogaard, who led the research team from Aarhus University and Aarhus University Hospital in Denmark, in a statement.
The drug, known generically as romidepsin and under the brand name Istodax, is licensed to treat a type of cancer called T-cell lymphoma. In this study, however, it was investigated as a potential HIV therapy.
Human immunodeficiency virus (HIV) infection can be kept at very low levels by anti-AIDS drugs, but there is still no cure that can eradicate HIV from the body.
Some 35 million people worldwide are infected with HIV, and the global AIDS epidemic has killed 39 million since it began in the 1980s, according to the latest data from the United Nations AIDS program, UNAIDS.
Scientists working to find a cure know the virus can hide in a state of hibernation in cells called CD4 cells, which are part of the body's immune system.
CD4 cells cannot fight the AIDS virus themselves, but killer T-cells can if they are able to tell whether or not a CD4 cell contains the hibernating HIV.
Sharon Lewin, co-chair of the AIDS2014 conference in Melbourne Australia and a professor of infectious diseases who was not directly involved in this study, said the results of the study were significant and encouraging because they showed "we can wake up the virus reservoir and make enough of (it) to leave the cell, making it visible to an immune response".
The Danish team gave three once-weekly infusions of romidepsin to six HIV-positive adult patients who were already taking antiretroviral AIDS drugs and whose so-called "viral load" was undetectable.
They found that romidepsin increased the virus production in HIV-infected cells between 2.1 and 3.9 times above normal and that the viral load in the blood increased to measurable levels in five out of six patients.
"We have now shown that we can activate a hibernating virus with romidepsin and that the activated virus moves into the bloodstream in large amounts," Schmeltz Sogaard said in a statement about the results.
When the virus is activated and moves towards the bloodstream it leaves a trace on the outside of the infected CD4 cells, he explained. In principle, this means killer T-cells would be able to trace and destroy the HIV-infected CD4 cells.
The Danish team said the next step is a larger trial where the researchers will combine romidepsin activation of hidden HIV with an experimental vaccine called Vacc-4x being developed by the Norwegian biotech firm Bionor Pharma to strengthen the ability of T-cells to fight HIV.
(editing by Jane Baird)