Steve Connor: The battle against HIV is still far from won

The fact is that the human immunodeficiency virus is one of the most difficult infectious agents that medical science has ever faced and talk of a cure is almost certainly premature.

HIV is a retrovirus with the ability to reverse-engineer its genetic material so it can integrate itself in to the DNA of the patient. As one Aids scientist said many years ago: once you are infected with HIV, you areinfected for life.

Of course, the team led by David Margolis of the University of North Carolina at Chapel Hill must be aware that basing broad conclusions about the efficacy of their approach on just four patients is a dangerously risky strategy.

Proof that the drug, valproic acid, or some equivalent, actually works must await the outcome of much bigger clinical trials involving many hundreds if not thousands of patients.

That could take anything between five and 10 years, so - whatever the merits of the study - Aids patients will not see the benefit for many years. Unfortunately that means even if the drug turns out to be the cure it is said to be, most people in the world today with HIV will not live long enough to see it.

One of the many problems of HIV is it is a virus that attacks the very immune defences that have evolved over many thousands of years to allow the body to ward off invading assaults.

The roaming white cells of the body that patrol the outer perimeters of the body's tissues normally gobble up and digest such infectious particles but HIV uses them as Trojan horses to gain access to the deeper recesses of the immune defences. HIV infects more than one type of white blood cell so it is no good saying that a drug capable of destroying HIV in just one class of white blood cell is a potential cure unless you can also show that it works equally well in other types.

Dr Margolis and his team concentrate on the so-called T-cells of the immune system but do not mention the other form of white blood cells, the phagocytes or macrophages. It is those macrophages that become the Trojan horses.

Stating that the findings of the study in The Lancet suggest new approaches will allow the cure of HIV in the future is strong language for a medical journal. A cure means eliminating it completely from the body, something few Aids scientists would be prepared to admit is possible.