Immunisation against the Alzheimer鈥檚 protein can prevent memory decline in mice.
Mice engineered to develop a disease like Alzheimer鈥檚 developed fewer amyloid plaques and performed better on memory tests after regular injections with a protein vaccine.
The research, from two international teams of researchers, boost hopes that a version of the vaccine now in human trials will produce positive results. It also gives researchers a method for finding out when it is best to give the vaccine.
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But researchers caution that there are still many ways in which the human vaccine could fail. 鈥淭here are a whole slew of caveats,鈥� says Peter St George-Hyslop, a biologist at the University of Toronto who led one of the teams. 鈥淗umans may respond very differently.鈥�
Mice engineered to produce large quantities of the human Alzheimer鈥檚 amyloid protein Abeta develop heavy deposits of the protein in the brain. These resemble the senile plaques seen in autopsies of Alzheimer鈥檚 patients.
Immunisation with Abeta had previously been shown to reduce the plaque burden in the mice. But until recently no-one had detected a significant change in the cognitive abilities of the animals.
Now two teams, one led by St George-Hyslop, the other by Dave Morgan at the University of South Florida in Tampa, have found that the Alzheimer鈥檚 mice have trouble remembering the location of a platform in a milky pool.
Normal mice swim a straighter path to the platform each time they are dropped in the pool. But the amyloid mice in the late stages of disease behave almost as if they have never been in the pool before.
Regular injections of Abeta prevent this cognitive decline. A chemical irritant known as adjuvant injected with the protein stimulates the production of antibodies against Abeta which direct the immune system to clean out the brain.
Although the immunised Alzheimer鈥檚 mice were still a little slower than normal mice, the severe learning deficits never set in.
St George-Hyslop points out several caveats in making the leap to humans. There is no guarantee that the vaccine will elicit as strong an immune response in people. It is in the first phase of clinical trials by Elan Pharmaceuticals of South San Francisco.
Worse still, since Abeta is produced throughout the body, the immune system could attack healthy tissues. 鈥淥ne has to wonder whether it might cause a runaway auto-immune disease,鈥� says St George-Hyslop.
Elan scientist Dale Schenk was pleased with the findings: 鈥淭hey certainly bolster our confidence. But we still have to wait for data from humans.鈥�
More at: Nature (vol 408, p 975, 979)