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Researchers developing a vaccine against Alzheimer's disease have shown that it seems to stop mice with the condition from losing their memory, which boosts hopes that such vaccines could delay or prevent similar symptoms in humans. The vaccine also reduces the build-up of protein deposits in mouse brains - the other major indicator of Alzheimer's disease. The pharmaceutical company Elan, based in Dublin, Ireland, is poised to begin large-scale human clinical trials of a potential treatment based on the vaccine. But what works in mice does not always work in people and the vaccine will still have to prove its worth in a battery of further tests.

Peter St George-Hyslop of the University of Toronto in Canada and his colleagues and a second team led by Dave Morgan of the University of South Florida at Tampa showed that the vaccine reduces learning and memory loss as the mice age. Each group gave Alzheimer's mice learning and memory tests, in which the animals had to swim to a submerged platform. In one trial the platform was moved each day, testing short-term memory. The second trial investigated 'spatial-reference' memory by leaving the platform in one place and testing the mice once a month. Mice given the test vaccine developed fewer and smaller protein deposits in their brains and performed markedly better than unvaccinated animals in both types of memory test.

Whether the protein deposits actually cause dementia in people is unclear. Some researchers believe that preventing the deposits from forming should relieve the distressing mental symptoms, although others disagree. This research supports the hypothesis that the two are related, but other factors could still be involved.

A collection of research reports on this subject are included in the current issue of Nature Magazine.