A potential DNA vaccine for Alzheimer's disease has produced promising results in mice.
The vaccine was tested on mice
In tests, it helped cut levels of key amyloid proteins thought to cause the disease by up to 50% in some parts of the brain.
And unlike alternative vaccines in development, which use viruses, it produced no side effects.
The Japanese study appears in the journal Proceedings of the National Academy of Sciences.
Over-production of amyloid proteins are thought to trigger symptoms of Alzheimer's by forming clumps that litter the brain.
Previous studies have shown that it is possible to stimulate the immune system of mice to attack these plaques if they are immunised with amyloid protein.
This approach has been tested in preliminary trials on humans, but early results showed that the immune response was too strong, leading to damaging swelling of the brain, as well as plaque destruction.
New studies in humans are currently underway that hope to mobilise the immune response in a less aggressive manner so that plaques are destroyed, but brain swelling is avoided.
The latest approach, developed by a team at Tokyo Metropolitan Institute for Neuroscience, works by stimulating the body to produce small amounts of amyloid protein itself.
Mice are injected with naked DNA that codes for these proteins, rather than relying on a special virus to get it into the cell.
This has the effect of producing a more gentle immune response, and importantly the DNA has also been designed so that it is not capable of replicating itself by incorporating itself into the human genome.
In tests, the latest vaccine reduced the deposition of amyloid proteins by between 15.5% and 38.5% compared with untreated mice.
Deposition in specific areas of the brain - the cerebral cortex and hippocampus - was reduced 40%-50%.
The researchers suggest that DNA vaccines of the type they have produced could provide a cheap and effective strategy for treating Alzheimer's in future.
Dr Clive Holmes, of the Alzheimer's Research Trust, said the Toyko study held great promise.
He said: "This work represents a promising new line of vaccine development but more research would be needed to see if this could be replicated safely in humans."
Dr Susanne Sorensen, of the Alzheimer's Society, agreed that the fact that the vaccine appeared safe was significant.
She said: "The findings support the idea that a vaccine is our best hope for fighting this devastating disease for which there is currently no cure."