Scientists have harnessed the body's own natural defences against infection to make a treatment for dementia.
The scientists used the body's natural defence against disease
A German team, from Friedrich-Wilhelms University in Bonn, used proteins or antibodies produced by people against disease.
Five Alzheimer's disease patients treated with the experimental therapy showed improvement in tests.
More work is needed but the results are promising, said the authors in the Journal of Neurology, Neurosurgery and Psychiatry.
People with Alzheimer's disease have 'amyloid' deposits in the brain that are made up of a protein beta peptide.
These deposits get progressively worse and damage the brain tissue, leading to dementia.
Scientists have been looking at ways of blocking the action of beta peptide to prevent the build up of amyloid deposits using vaccines.
Now Dr Richard Dodel and colleagues believe they have found a way to do this, using the body's own natural defence system, in humans.
When the body encounters a disease or infection it produces complex protein molecules called antibodies to seek out and destroy the invasion.
The researchers isolated antibodies against beta peptide and injected these into patients with early Alzheimer's disease on a monthly basis for six months.
To monitor the effect of this experimental treatment, the scientists measured the levels of beta peptide in the cerebrospinal fluid, which bathes the brain, at the beginning and end of the study.
They also tested the patients' brain function for things like memory, which is affected by dementia.
At the end of the six months, levels of beta peptide in cerebrospinal fluid fell by 30%, and the level of beta peptide in the blood shot up 233%, suggesting that the treatment was working.
Although brain, or cognitive function improved only slightly in four patients, it did not worsen, which would have been expected after six months.
Also, mental tasks improved in three patients and stayed the same in the other two.
The scientists said although definitive conclusions could not be drawn on the strength of a study of five patients, their findings warranted further detailed investigation, and added weight to the experimental evidence.
In an accompanying editorial, Alzheimer's experts Professor Philip Scheltens and Dr Erik Hack from The Netherlands said: "Larger studies are needed to confirm that this treatment can stabilise or even improve cognitive functions in Alzheimer's disease."
But they said the study highlighted "a novel and interesting" treatment option for Alzheimer's disease which seemed "worthy to be explored".
Professor Clive Ballard from the Alzheimer's Society said: "Whilst this is very encouraging, the safety and effectiveness of this specific type of vaccine treatment needs to be carefully examined in a larger trial."
He said there had been a lot of excitement about treating Alzheimer's disease using the immune system.
He said an approach which used a vaccine to make the body produce antibodies against amyloid proved to be very effective in animal studies.
This led to a clinical trial involving about 200 people with Alzheimer's disease, he said.
"Unfortunately, although the vaccine appears to clear some of the protein from the brain, a substantial minority of participants in the trial developed a serious complication called encephalitis (inflammation of the brain), with two people dying.
"Therefore a lot of effort has been directed at trying to further develop this vaccine treatment approach to enable it to be used safely," he said.
In the current study, none of the five patients had major side effects.
Dr Dodel said his approach should not encounter these problems because the antibodies are given directly to the patient in a "passive" way rather than encouraging the body to make its own antibodies in an "active" way.