The treatment uses fragments of DNA from the TB microbe to stimulate the immune system and ward off infection. It is a novel approach that is currently being tried with a range of diseases including Aids and malaria.

TB kills about three million people every year. It is estimated that the bacterium that causes the disease, Mycobacterium tuberculosis, is carried by over a third of the world's population.

Although there are antibiotics available, problems of drug resistance, and the sheer cost and availability of long-term medication in many parts of the world, mean that new strategies for tackling the disease are being sought.

Disabled bacterium

The best approach, of course, is prevention, by means of vaccination, and many people will be familiar with the BCG injection. But such vaccines are not always entirely effective.

The research team are hoping for even better results from their new DNA vaccine. Unlike the BCG, which is based on a disabled version of the whole bacterium, the new vaccine incorporates just specific pieces of DNA taken from the microbe.

The proteins which are created in the body using these bits of DNA will hopefully trigger an attack on the disease by the immune system, and provide the desired protection against future infection.

In research published in the Journal Nature, mice infected with TB showed a marked decline in their levels of infection after being given the DNA vaccine. There was evidence that the mice's bodies started to employ a far more effective type of immune response.

Better protection

Dr Doug Lowrie, from the UK's National Institute for Medical Research, says the studies undertaken by the team suggest they are on the trail of an improved treatment for existing infections as well as a promising new method of vaccination.

"We had in mind that we might be heading towards something that would prevent infection," he says. "But during the studies, it became apparent that we'd stumbled on something which would actually change the immune system in infected animals and possibly infected people. This would enhance their resistance to the disease and improve their treatment."

If all goes well, the vaccine could be used in clinical trials for humans early in the next millennium.

"If we were are extremely lucky and the vaccine that we have at the moment does not need much modifcation, we might be in clinics within one or two years, perhaps," he told the BBC.

"The first application is likely to be in those patients who are dying of a multidrug-resistant tuberculosis where there is really nothing else on offer."

Clinical trials

DNA vaccines are a new idea, and are not yet in general use.

But they are seen as a tool of great potential that could provide a means of combating many illnesses for which there are, at present, few effective treatments.

"There are about half a dozen different clinical trails, in different parts of the world, against a range of different diseases, things like influenza, malaria, HIV which causes AIDS, hepatitis B, and herpes.

"There is some caution about how effective they're likely to be. Perhaps the most encouraging results have come from potential vaccine candidates against malaria, where the immune response has looked very encouraging"