Cocktails of anti-HIV drugs have become the norm to suppress the virus in developed countries.

They disable two viral enzymes and have transformed many patients' lives.

But researchers think it may be possible to train the immune system to do this without the need for drugs.

Animal tests

Tests in animals have shown that stopping the therapy for two weeks can keep the virus at undetectable levels in the blood stream for up to 145 days.

The virus appears to be under control without drugs in some cases

Anecdotal evidence suggests a therapy break can have the same effect in humans, but scientists want to launch trials to gather proof.

The possibility of beneficial breaks was discussed at the Sixth Conference on Retroviruses and Opportunistic Infections in Chicago.

The debate is reported in New Scientist magazine.

Doctors presented plenty of animal and anecdotal evidence, but that is not proof enough to change treatment regimes.

The breaks appear to boost the performance of the cytotoxic T lymphocyte (CTL) immune response.

CTLs are white blood cells that kill other cells infected with a virus. As such, they are crucial in the fight against HIV.

Keeping the virus at bay

Dr Franco Lori told the conference about the case of an HIV patient in Berlin.

The patient started treatment on three types of anti-HIV drugs soon after he became infected.

Scientists believe the approach will succeed best when treatment starts soon after infection

However, due to medical complications, the treatment had to be stopped twice. It was later stopped altogether.

Yet two years on, levels of HIV in his blood are negligible.

Dr Lori believes the breaks in treatment allowed a CTL response strong enough to contain the virus.

He is researching the phenomenon at the Research Institute for Genetic and Human Therapy in Washington DC.

His experiments with monkeys bear out his theory.

They are infected with SIV, a similar virus found in animals.

Using a stop-start approach to the triple drug therapy, Dr Lori kept the virus at undetectable levels in their blood for 145 days.

Trials with humans

Another researcher, Dr Bruce Walker, is looking for more concrete evidence.

Dr Walker, of Harvard Medical School, is performing a small trial of the same technique on human patients.

He hopes to see if the immune system can be trained to controol the virus by stopping treatment for two weeks at a time.

He leaves a break of about a month between each treatment holiday.

And Bernard Hirschel, of Geneva University Hospital, is planning a trial with 100 patients, subject to the approval of an ethics committee.

But some doctors fear a stop-start approach could lead to the virus developing resistance to anti-HIV drugs.

Dr Paul Johnson, of the New England Primate Centre, thinks this is unlikely so long as all three therapies are stopped at the same time.

The real problem is with patients taking the correct doses.

Although the evidence so far looks promising, researchers are urging caution.

Luc Perrin, head of clical virology at Geneva University Hospital, told New Scientist: "We should be doing these experiments, but we should be clear that's what they are - experiments, not proven treatments."

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The original of this article can be found at http://news.bbc.co.uk/hi/english/health/background_briefings/aids/newsid_302000/302897.stm.

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