A US study using monkeys has found that the immune system can benefit from interrupting drug treatment regularly for short periods of time.

However the researchers have warned that people with HIV must not stop taking their prescribed medication except on the advice of a doctor.

Treatment for HIV generally involves taking a daily combination of antiretroviral drugs, which can have a variety of side effects.

The treatment suppresses the virus in the body and stopping taking the pills usually leads to a return of the virus.

It seems we can stimulate the immune system to better control the virus, which is a completely different way of looking at treatment

Dr Franco Lori, Research Institute for Genetic and Human Therapy

But Dr Franco Lori from the Research Institute for Genetic and Human Therapy in Washington DC has been investigating whether interruptions in treatment might actually boost the immune system.

"Our results suggest that patients might be able to take fewer drugs, which is an attractive possibility in itself," he said.

"On top of that, it seems we can stimulate the immune system to better control the virus, which is a completely different way of looking at treatment."

His research began after a patient was identified in Berlin who stopped his drug treatment on a number of occasions and then ceased it altogether, to find his immune system was continuing to suppress the virus on its own.

According to the journal Science, the research team infected rhesus macaques with the monkey version of HIVand waited until they developed AIDS.

Six monkeys were treated continuously with antiretroviral drugs, a second group was given no treatment and the third group was treated with the drugs on a three weeks on, three weeks off cycle.

Drugs were stopped after 21 weeks when both groups of monkeys receiving treatment had similarly low levels of HIV in their bloodstream as well as similar levels of immune cells known as CD4 T lymphocytes.

Free from virus

SIx months later it was found that the virus had returned in the monkeys that had been given the continuous treatment, while those receiving intermittent treatment were virtually virus-free.

The level of CD4 cells in this group has also stayed almost the same.

A further test was conducted on an immune cell, CD8 T lymphoctyes, which showed vigrorous activity in the monkeys receiving the intermittent treatment.

Dr Lori and his colleagues believe that the treatment had trained the immune system to control the virus and that the pattern could be replicated in humans.

The disease and the individual response to it varies enormously so it is impossible to make conclusions from such a small sample size

Terrence Higgins Trust

While it might not be possible to get rid of HIV in the body altogether it may become more like the herpes virus, which the immune system can successfully suppress most of the time.

But leading HIV and AIDS charity, the Terrence Higgins Trust has reiterated the warning that patients must never stop taking HIV medication unless advised to do so by a doctor.

"The disease and the individual response to it varies enormously so it is impossible to make conclusions from such a small sample size," a spokesperson said.

He pointed out that small developments are being made all the time in HIV drug regimens.

"The thing is no human would ever enter a trial such as this," he added.