AN EXPERIMENTAL drug helped monkeys with a form of the Aids virus control the infection for more than a year, suggesting it may lead to a vaccine for people, or even a cure.
Researchers said Cytomegalovirus (CMV) works by priming the immune system to quickly attack the HIV virus when it first enters the body, a point at which the virus is most vulnerable.
Dr Louis Picker of the Oregon National Primate Research Centre, whose study appears in the journal Nature, said he thinks it will be possible to have a vaccine ready to test in people within three years.
CMV enables the immune system to be constantly on the alert for HIV.
Researchers used different versions of the vaccine against a monkey form of the Aids virus, SIV (Simian Immunodeficiency Virus) with outstanding results.
More than half the rhesus macaques treated responded to the point where even the most sensitive tests detected no signs of SIV.
To date, most of the animals have maintained control over the virus for more than a year, gradually showing no indication that they had ever been infected.
Unvaccinated monkeys infected with SIV went on to develop the monkey equivalent of Aids, caused by the collapse of their immune systems.
The findings suggest the vaccine could be effective enough to rid the body of immunodeficiency virus completely, according to the scientists writing in the journal Nature.
Conventional antiretroviral therapies are able to control HIV infection, but cannot clear the virus from its hiding places within the immune system's white blood cells.
Dr Picker said: “The next step in vaccine development is to test the vaccine candidate in clinical trials in humans.
“For a human vaccine, the CMV vector would be weakened sufficiently so that it does not cause illness, but will still protect against HIV.”
CMV belongs to the herpes family of viruses, and like other members of the group, never leaves the body once an infection has occurred.
An estimated half of all adults in the UK carry CMV but suffer no or few symptoms. The virus is spread through bodily fluids such as saliva and urine.
When symptoms do occur, they are similar to those of flu including a high temperature and swollen glands and tiredness. People with weakened immune systems can have a more severe response.
“What’s exciting about these findings is that for the first time a vaccine candidate has been able to fully control the virus in some animals,” said Dr Wayne Koff, chief scientific officer at the International AIDS Vaccine Initiative (IAVI), which helped fund the research.
Koff said the findings also suggested the possibility that the immune system may eventually eliminate the virus altogether.
“This research gives us potential clues as to how we might design an HIV vaccine for humans that would provide the same type of control,” he said.
There is no cure for Aids, but cocktails of drugs can keep the disease at bay for many years.
The human immunodeficiency virus that causes Aids infects 33.3million people globally, according to the United Nations agency UNAIDS. It has killed more than 25 million people.
Because it is spread in so many ways - during sex, on needles shared by drug users, in breast milk and in blood - there is no single easy way to prevent infection.
A vaccine is the best hope, and many drug companies and scientific research groups are working on various ways to try to develop one.
“The breakthrough here is in using a viral-delivered vaccine that persists - essentially using an engineered virus to thwart a pathogenic virus,’ said Robin Shattock, a professor of mucosal infection and immunity at Britain’s Imperial College, who was not involved in the research.
“Before this, scientists had pretty much given up on the idea of a vaccine that could control HIV replication. This puts it firmly back on the agenda.”
Efforts so far to make an Aids vaccine have not been successful, but a 2009 study in Thailand involving 16,000 people showed for the first time that a vaccine could safely prevent HIV infection in a small number of volunteers.
Dr Picker said the next step is to make a weaker version of the CMV virus to make sure it does not cause any problems in people.
“The concern would be if we move a virus that is not modified that in some small number it might cause disease,” he said.