Aids vaccine is brought a step closer: Injecting HIV genes into patients' cells aims to stimulate body's immune system

A RADICAL new approach in medical science has brought the prospect of a vaccine against Aids a step closer.

Conventional vaccines rely on injecting the infective agent itself. The new 'genetic inoculation' technique relies on injecting genes of the Aids virus into the cells of the patient.

The idea, which is similar to gene therapy, is that the body will manufacture important bits of the virus that will stimulate the immune system to produce an effective defence against any future attack from HIV.

Researchers are also investigating methods of producing genetic vaccines against malaria, which is caused by a blood parasite, and cancerous tumours, which could be attacked by a type of genetic therapy.

Scientists in the United States believe the approach is more than a pipedream with the publication today in the science journal Proceedings of the National Academy of Sciences of the first results of tests of a genetic vaccine on laboratory mice.

David Weiner, an immunologist at the University of Pennsylvania, said the results showed the approach was safe and capable of producing the 'right sort' of immunity. He emphasised, however, that there was a long way to go before declaring an effective Aids vaccine. 'We have only done the initial work. This is not an Aids vaccine.'

Traditional methods of making vaccines use either live viruses, which have been rendered harmless or 'attenuated', or viruses that have been killed yet retain important physical features which the immune system can recognise and produce effective antibodies against. The disadvantage of live, attentuated viruses is that there is always a possibility that they could revert to being harmful. With the Aids virus, which mutates rapidly and causes disease many years after infection, a live, attenuated virus is considered too dangerous to be used.

Most effort has therefore concentrated on using inactivated HIV, or bits of the virus's protein, as a vaccine. One of the many fears of this approach, however, is that such a vaccine would not generate the right sort of immunity because it does not behave like an infective agent.

Dr Weiner said the genetic vaccine he has tested has shown itself to be both safe and capable of generating an effective immune response - one where the all-important 'killer cells' of the immune system are mobilised into an attack.

The prototype vaccine itself is made from the genes of HIV that the virus uses to orchestrate the manufacture of its envelope proteins, which form its outer 'coat'. Dr Weiner and his colleagues injected the genetic material into laboratory mice. The animals then began to make viral proteins under the command of the genes. The results indicated the approach 'is a very important avenue of research', he said.

Dr Weiner said there were plans to take the research further with tests on monkeys. Clinical trials on humans could then be considered, but he could not say when this was likely.