Vaccine for Alzheimer's passes crucial safety test

The first vaccine to show promise against Alzheimer's, the degenerative brain disease affecting up to 500,000 people in the UK, has passed an important hurdle in human safety trials. Initial results from a phase one trial of the vaccine in the US, designed to test the toxicity of the vaccine, showed "no obvious safety concerns", researchers reported yesterday.

The first vaccine to show promise against Alzheimer's, the degenerative brain disease affecting up to 500,000 people in the UK, has passed an important hurdle in human safety trials. Initial results from a phase one trial of the vaccine in the US, designed to test the toxicity of the vaccine, showed "no obvious safety concerns", researchers reported yesterday.

Further safety trials are to be conducted in 100 patients in the US and the UK, but researchers said the early results, presented at the World Alzheimer Congress in Washington DC, were highly encouraging. However, it will be at least two years before they will know whether the vaccine, already shown to be effective in mice, can help people with Alzheimer's, the most common form of senile dementia.

The scientists, from Elan Pharmaceuticals, in California, reported a year ago in the science journal Nature the results of experiments on transgenic mice - mice genetically altered to develop the distinctive protein deposits called "plaques" seen in the brains of people with Alzheimer's disease.

An injection of the vaccine, a synthetic version of the naturally occurring beta amyloid protein, significantly reduced the formation of the plaques. Although the finding was impressive, some scientists warned at the time that the vaccine might not prove safe in humans. That fear now looks as though it may have been dispelled. The strongest theory about the cause of Alzheimer's is that the plaques interfere with the function of nerve cells in the brain and cause nerve cell death, accounting for the mental deterioration associated with the disease. However, it is not yet known whether the plaques are the result or the cause of the disease process.

Harry Cayton, director of the Alzheimer's Disease Society in the UK, said the research was "potentially very interesting" but warned against raising expectations. "They have gone very quickly from virtually theoretical stuff in mice to human trials. But we don't know if the beta amyloid plaques are the symptom or the cause of the disease. Mice get the plaques but they don't actually get Alzheimer's disease so we don't know if clearing the plaques will have any effect on Alzheimer's in humans," he said.

The number of people affected by Alzheimer's is likely to rise by 50 per cent over the next 40 years because of the ageing of the population, and there is currently no cure. Some drugs have been shown to slow progression of the disease but not to halt or prevent it. Dale Schenk, vice-president of Discovery Research at Elan, said: "We are extremely pleased with the progress of our phase one trials, which have shown that [the vaccine] is well tolerated by the patients. During the course of our research, we also developed a greater understanding of how the vaccine works to clear amyloid plaques out of the brain and prevent additional plaques from forming.

"Amyloid plaques act as a brain invader. We are optimistic that we can attack this invader at its source and eventually help the millions of people and families worldwide who are living with this devastating disease," he added.

The scientists confirmed, while conducting additional animal studies, that the vaccine leads to an immune response that increases the clearance of beta amyloid plaques from the brain. Antibodies were formed which bound themselves to the plaques and allowed them to be engulfed by other immune system defenders called microglial cells.

Bill Thies, vice president of medical and scientific affairs at the Alzheimer's Association in the US, said: "Just a few years ago, talk of a potential vaccine for Alzheimer's disease would have been viewed with much scepticism and disbelief. Announcements like this that are grounded in solid scientific research give us tremendous hope."