Vaccine against Alzheimer's disease may still be on the cards

May 10 2005

A new, but modified, trial of an Alzheimer's vaccine has begun in the U.S. despite an earlier one being abandoned in 2002 due to safety concerns.

The earlier trial was stalled after about 6 percent of participants developed a dangerous brain inflammation, encephalitis, but researchers continued to monitor the remaining patients for up to a year after their last injection and found some encouraging results.

Researchers at the University of Michigan found that participants whose immune systems had mounted a high antibody response to beta-amyloid levels in the brain performed better on memory tests than people who had received a placebo.

They also experienced an unexpected decrease in brain size, possibly linked to clearance of disease-causing proteins from the brain.

In the halted trial, 59 of the 300 participants who received at least one injection developed significant quantities of antibodies against beta amyloid in their blood.

In general, those who developed antibodies also displayed stabilization of memory and scored better on certain neuropsychological tests evaluating memory than the placebo group. Furthermore, among those patients who did develop antibodies, those who produced relatively high levels achieved better results on memory tests than those who developed lower levels.

The new study also found that patients who had a good antibody response and good memory stabilization had less brain shrinkage than patients unresponsive to the immune-based therapy. In fact, they experienced brain shrinkage above and beyond that of unresponsive individuals.

The new trial is incorporating the successful elements of the old trial without the safety hazards and has been encouraged by autopsies results which that show that the participants who died of causes other than encephalitis seemed to have successfully cleared some beta amyloid from their brain.

Researchers are injecting participants with already prepared antibodies, instead of beta amyloid itself, a method called passive immunization instead of active immunization, in the hopes of eliminating previous problems.

The trials are funded by two drug makers, Elan Corp. and Wyeth Pharmaceuticals.