A vaccine that triggers the immune system to fight against the plaque-building protein implicated in Alzheimer's disease may still be a viable option in the future for treating -- or perhaps even preventing -- the devastating disease, according to new research.
An earlier study of the experimental Alzheimer's vaccine was halted due to safety concerns in 2002 after 6 percent of the participants developed brain inflammation.
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 preserves cognition."
Round Two 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 percent 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.
Better Performance on Memory Tests
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.
By Jennifer Warner, reviewed by Brunilda Nazario, MD
SOURCES: Gilman, S. and Fox, N.Neurology, May 2005; vol 64: pp 1553-1562, 1563-1572. News release, University of Michigan Health System.
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