While an experimental
vaccine for Alzheimer’s disease may work, it was found
to cause life-threatening side effects in some cases.
It is thought that
the vaccine works by causing the body’s immune system
to fight against abnormalities in the brain known as plaques.
These plaques are thought to cause some of the symptoms of
Alzheimer’s disease including forgetfulness and confusion.
However, the vaccine may cause an immune overreaction causing
severe brain swelling.
Some six percent
of participants in a trial of the vaccine suffered from severe
brain swelling, leading the vaccine manufacturer, Elan, to
call off the trial.
Researchers examined
the brain of a woman who had taken the vaccine and died after
a fall in order to investigate the side effect. They found
fewer plaques in the woman’s brain than in Alzheimer's
patients who did not receive the vaccine.
However, researchers
also found immune-system cells known as T cells in the woman’s
brain. T cells are not normally in the brains of patients
with Alzheimer’s, so the cells’ presence suggests
an overreaction of the immune system that may have harmed
normal brain tissue and caused inflammation, according to
researchers.
An Elan researcher
leading the company’s effort to develop an Alzheimer’s
vaccine said that, despite setbacks, the company hopes to
begin trials of an altered version of the vaccine later this
year, and pointed out that the vaccine may have actually removed
plaque from the brain.
However, other
experts say that some patients with Alzheimer’s have
very few plaques, so it can’t be concluded that the lower
level of plaque was due to the vaccine.
Moreover, it has
not been proven that reducing Alzheimer’s-related plaque
improves symptoms in patients with Alzheimer’s disease.
Nature
March 17, 2003
