Experts have issued a cautious welcome to results showing a vaccine could help slow the progress of Alzheimer's disease.
Scientists were working on a vaccine for Alzheimer's
Although the Swiss study had to be stopped early after some patients developed a dangerous brain inflammation, it did show some positive results.
Around 385,000 people in the UK are estimated to have Alzheimer's, the most common form of dementia.
It gradually destroys the brain, causing memory
loss. There is no cure, but some drugs can
temporarily slow the disease's progress.
An international team of researchers gave the vaccine, called AN-1792, to 300 patients with Alzheimer's.
If these results are confirmed in the report of the whole study then this would be very powerful evidence that the vaccine is having a real effect on the Alzheimer's disease in these people
Dr Richard Harvey, Alzheimer's Society
It targets the beta amyloid proteins which form plaques in the brain of someone with Alzheimer's.
Patients given the vaccine began to produce antibodies designed to attack beta amyloid.
But the study was halted in March 2002 after 17 patients developed the potentially fatal brain inflammation meningoencephalitis.
'Not a cure'
Researchers at the University of Zurich then studied 30 of the 300 patients,including three with encephalitis.
They found 20 had generated antibodies against beta-amyloid and seen a slow-down in the development of their condition, including two who had developed the encephalitis.
But the researchers stressed the vaccine was not a cure for Alzheimer's.
Dr Roger Mitsch, who led the study, said: "Patients with high levels of antibodies were essentially protected from disease progression over the one year study period.
"This is the first time that antibodies against beta amyloid were shown to be effective in slowing the course of Alzheimer's disease."
Dr Richard Harvey, head of research at the UK's Alzheimer┐s Society, said: "It's very exciting to see the first glimpse of the results of the large scale trial of the anti-Alzheimer vaccine.
"However, great caution is needed as the results presented here represent only a 10% sample of those who took part in the trial - and a small sample makes it much more likely that the result seen is simply due to chance and not a real effect."
But he added: "Nevertheless, if these results are confirmed in the report of the whole study then this would be very powerful evidence that the vaccine is having a real effect on the Alzheimer's disease in these people."
Dr Harvey said a full study would have shown other important effects, such as the rate of brain tissue loss.
He added: "Showing that the vaccine had slowed the loss of brain tissue associated with Alzheimer's disease would be the first evidence of a true disease modifying therapy.
"But despite safety problems with this initial version of the vaccine, vaccine/immune based therapies still hold tremendous potential for delivering an effective treatment for this terrible disease."
The research is published in the journal Neuron.
'Test tube benefits'
A second study by Canadian researchers on mice has suggested the drug lithium, usually used to treat manic depression, can help stop the build up of the plaques
Dr Harvey said the research, published in the journal Nature, said the study confirmed previous findings.
He said: "Lithium as a drug is highly toxic and not easy to use, requiring regular monitoring of blood levels.
"Whether the benefits seen in the test tube will translate into real life, and then tip the risk/benefit balance remains to be seen."