A vaccine against Alzheimer's was one step closer to reality after scientists succeeded in preventing the accumulation of toxic brain proteins associated with the disease.
Experiments on mice have shown that the DNA injected into the skin can delay the onset of Alzheimer's without a serious side effect.
Scientists said the findings published in the journal Alzheimer's Research and Therapy could pave the way for clinical trials with human patients.
Two types of toxic protein or protein building blocks are thought to play an important role in Alzheimer's, beta-amyloid and tau.
Beta-amyloid accumulates in adhesive clusters in the brain and is a characteristic distinguishing feature of the disease seen in post-mortem examinations.
Tau is a protein that produces destructive "nodes" in nerve cells. Some studies suggest that the two are interdependent and are related to beta-amyloid, which promotes the formation of tau disturbances.
The novel vaccine comprises DNA coding for a part or peptide of the beta-amyloid protein building block.
In the study, the vaccine triggered an immune response that did not only lead to a 40% reduction in beta-amyloid deposition, but also to reduce tau formation by 50%.
The study was performed on genetically engineered mice to develop the murine equivalent of Alzheimer's disease.
The biggest obstacle to the development of effective Alzheimer's vaccines is to find safe ways of introducing them into the body.
The previous experimental vaccine developed in the early years of 2000 caused brain swelling when tested in humans in some patients.
The new vaccine is injected into the skin rather than the muscle, resulting in a different immune response.
Researchers, if repeated in humans, the effects of mice will have a "major therapeutic value".
"If the onset of the disease can be postponed in five years, it would be enormous for patients and their families," said Doris Lambracht-Washington.
"The number of cases of dementia may drop by half," he said.