Alzheimer's Vaccine Inching Toward Reality
Despite Setback, Vaccine for Alzheimer's Disease May One Day Be a Treatment Option
May 9, 2005 -- A to
fight against the plaque-building protein implicated in may still be a viable option in the future for treating --
or perhaps even preventing -- the devastating disease, according to new
An earlier study of the experimental Alzheimer's vaccine was halted due to
safety concerns in 2002 after 6% of the participants developed brain
But two new studies that followed the participants suggest that the approach
may slow the memory loss associated with Alzheimer's disease by reducing the
buildup of beta-amyloid plaques in the brain.
"The idea of inducing the immune system to view beta-amyloid as a
foreign protein, and to attack it, holds great promise," says researcher
Sid Gilman, MD, a neurologist at the University of Michigan Health System, in a
news release. "We now need to see whether we can create an immune response
safely and in a way that slows the progression of Alzheimer's disease and
Round 2 for Alzheimer's Vaccine
Although the safety phase of the study of the vaccine was halted in 2002,
researchers continued to follow the participants, and their findings appear in
two studies published in this month's issue of Neurology.
About 300 men and women with mild to moderate Alzheimer's disease received
one to three injections of the vaccine before the study was stopped, and 72
received a placebo.
Brain scans using magnetic resonance imaging (MRI) to measure changes in
brain volume were performed at the start of the study and again after 12 months
or after early termination.
Researchers found that of those who received the vaccine, about 20%
developed antibodies to beta-amyloid protein; that indicates the immune system
of the participants had launched an attack against the plaque-causing protein
in the injected vaccine. All but two of these 59 "immune responders"
had received two doses of the vaccine.
These immune responders also experienced a decrease in brain volume,
according to MRI scans. Researchers say this decrease may reflect a reduction
in plaque buildup, but more study is needed to confirm this effect.
In addition, immune responders also performed slightly better on memory
tests than those who received the placebo, but there were no significant
differences on five other measures of dementia between the two groups.
A small subgroup of those who responded to the vaccine also had lower levels
of a protein called tau in the spinal fluid compared with those who received
the placebo, which may indicate a slowing in the progression of Alzheimer's
disease. The tau protein in Alzheimer's disease is believed to be responsible
for the death of nerve cells that process, store, and retrieve information.
Safety Concerns Merit Further Research
The most common side effects associated with the vaccine were headache,
brain inflammation (encephalitis), and confusion.
Researchers say that the 18 patients who developed brain inflammation also
had higher levels of beta-amyloid antibodies than the others in the treatment
group, but these levels were highly variable and other mechanisms may be behind
this side effect.
The researchers say a change in the vaccine's formulation may have been
responsible for this complication.
Finally, researchers say the results of these studies suggest that benefits
of the experimental Alzheimer's vaccine may be achieved without the risk of
brain inflammation and warrant further study.
Both of the studies were funded by Elan Corporation and Wyeth
Pharmaceuticals. Wyeth is a WebMD sponsor.