Imagine your immune system suddenly goes haywire and no longer recognises your cells as your own. Instead of protecting you from disease, it starts attacking your own tissues, damaging cells and wreaking havoc on your lungs, joints and blood vessels, producing unpleasant skin rashes, pain and headaches. For the 40,000 lupus sufferers in the UK, this is exactly what happens.

Nine times out of 10, this autoimmune condition, which also increases the risk of miscarriage for female sufferers, can be successfully treated with a carefully tailored drug regime. But for some, drugs have little effect.

Now doctors in Europe and the US believe a revolutionary new treatment could be the answer. The technique, which involves wiping out the natural immune system and creating an entirely new one, is known as a stem cell transplant - and its pioneer, Dr Richard Burt, director of bone marrow transplantation at Chicago's Northwestern Memorial Hospital, says the seven patients he has treated so far have made a complete recovery.

'We treated our first patient two years ago,' he says. 'So far she has no signs of lupus and no antibodies in her blood, which shows she is clear of the disease. Of course, it could come back at any time. But we hope that once we get the immune system back on line again, it will stay that way.

'Although lupus sufferers have a genetic susceptibility to the disease, it's not inevitable. Something, we don't yet know what, must trigger it. If that trigger has passed, it's possible that a new immune system will cure sufferers for ever.' But it is not a treatment for the faint-hearted. Side-effects can be serious, even fatal. The patient is given a cocktail of drugs and radiotherapy to wipe out the immune cell. First, however, stem cells - the primitive cells responsible for producing the immune cells that make up our defence system - must be removed from the patient's blood so that they too are not destroyed. This is done by filtering the patient's blood supply out from one arm and returning it, minus the stem cells, through the other.

When all the immune cells have been eliminated, the stem cells are returned to the body and start manufacturing a new immune system - one that no longer sees the body as an enemy.

For sufferers of autoimmune diseases such as lupus, multiple sclerosis and rheumatoid arthritis, it's a second chance - an opportunity to wipe the slate clean. But it comes at a price. 'The biggest risk is opportunistic infection,' says Dr Burt. 'We haven't had any problems yet, but it's a serious risk.' It probably takes a couple of years of get the immune system back to full strength again and, with defences lowered, any infection becomes a serious threat. However, the body does have some protection soon after treatment. Within 10 days, neutrophils, cells that destroy bacteria, are back in circulation. And just to be on the safe side, says Dr Burt, patients are also given antibiotics and anti-fungal treatments.

The transplant does mean that all the immunity you acquired as a child is wiped out. Your body no longer has any memory of contact with diseases such as chickenpox or mumps, which means having all those childhood vaccinations again.

But in the long run, it's possible that the immune system will work better than ever. 'Lupus sufferers often have difficulty fighting off infections because their immune system is malfunctioning. After this treatment, it often works better than it did before.' A stem cell transplant may also help sufferers of multiple sclerosis: 'It doesn't repair damage already done,' says Dr Burt. 'But it does appear to halt progression.' Further research is needed before this treatment becomes routinely available for either disease. At present, stem cell transplants are not available in the UK for lupus patients.

However, British lupus expert Dr Graham Hughes from St Thomas' Hospital, London, says it's likely that they will be soon - for the small number of patients who simply don't respond to drug therapy: 'It's a risky treatment, so we would always be cautious about who we treated. But as the technique improves and it becomes safer, I'm sure we'll start using it on more lupus sufferers.'

• For further information, call Lupus UK, St James' House,
on 01708 731 25.