'Cocktail' opens new chapter on Aids

Scientists are excited by possible treatment for the killer disease, reports Liz Hunt

Scientists are heralding a "new chapter" in the history of the Aids pandemic, with the advent of a potent drug cocktail that may drastically reduce the level of HIV in the blood, and even stop the virus from replicating.

On the final day of the 11th International Conference on Aids in Vancouver, Canada, the less cautious were predicting that a cure was in sight for the disease which has killed almost six million people so far.

Only time will tell whether the drug cocktail merely prolongs symptom- free life while failing to halt the ravages of HIV in the long term.

Meanwhile doctors and patients in the developed world - the only ones likely to benefit from expensive new drugs - are sifting through the hype and politics of Aids research to determine the value of the claims.

More is known about HIV than any other virus, but 15 years' undivided attention from some of the best brains in the world, and billions of dollars' worth of investment, have failed to deliver a cure. The scientists are as conscious of this as the pharmaceutical companies, which have to keep their share-holders happy. Hence the high-profile launch of new drugs used in the cocktail, known as protease inhibitors, in Vancouver this week, supported only by the most preliminary of studies.

The study which prompted so much excitement has been running for less than a year at the Aaron Diamond Aids Research Center in New York and involves 12 patients, gay men with an average age of 34.

They had all become infected with HIV within three months prior to the trial, so there had been little time for the virus to mutate. None of the men had received any previous treatment, which could also have confounded the results.

The cocktail consisted of AZT (Retrovir, the first drug licensed to treat Aids) and 3TC, both made by Glaxo-Wellcome, and Norvir, one of a new class of drugs, protease inhibitors, which have become available in the last six months. This is made by Abbott Laboratories.

Protease inhibitors block an enzyme crucial to the multiplication of HIV, while AZT and 3TC work at an earlier stage. The idea behind the therapy is that HIV is delivered a "one-two" punch, doctors say.

Up to nine months after treatment began, HIV levels in nine of the men had fallen to below the level of detection, and their white blood cell counts had risen significantly.

Dr Martin Markowitz, who presented the study at the conference, said: "If you think of HIV as a raging fire ... we put out the fire. Cure is a dangerous word. What this means is that we have turned off viral replication."

Of course, the only way to know for sure if replication has been halted is to stop the drugs, and this may happen in September, though it does pose ethical problems for the scientists. How can they withdraw a treatment which is having some impact on their patient's disease?

Words like "eradicate" have been bandied about, but there is no evidence that the triple therapy has achieved this. HIV is known to hide in other parts of the body, such as the nervous system and lymph tissue, when it is no longer detectable in the blood. Samples of lymphoid tissue removed from the men will be tested shortly.

Apart from the risk of HIV strains emerging which are resistant to all three drugs in the cocktail, stopping the treatment may produce a rebound effect - an accelerated replication of the virus - with devastating effects.

Dr David Ho, one of the world's top Aids researchers and director of the Aaron Diamond Center, has stressed that the triple therapy approach is an experiment only, and that no one has been cured to date.

What excites him is that the most virulent aspects of HIV appear to be knocked out by the cocktail, and this raises the question: "how long would we have to continue with the drugs to kill the virus?

The answer, based on analysis and the limited experience so far, is one to two years, Dr Ho believes. However, longer studies involving many more HIV-infected people are necessary, and the long-term result may prove to be different.