There's no indication that the effect made any noticeable difference in the patients' day-to-day functioning. The study wasn't set up to look for that.
But the memory result was surprising and encouraging for the general idea of using the immune system to attack Alzheimer's, said researcher Sid Gilman.
"I think there's a positive signal here," said Gilman, a professor of neurology at the University of Michigan.
The vaccine was intended not to prevent Alzheimer's, but to treat it. The experiment was halted in early 2002 after 18 of 300 participants developed brain inflammation. The vaccine formulation has been abandoned, but the general immune-system strategy is still being pursued.
Gilman spoke in a telephone interview before presenting the vaccine results Wednesday at the International Conference on Alzheimer's Disease and Related Disorders in Philadelphia. The study was sponsored by Elan Corp., based in Dublin, Ireland, and Wyeth Pharmaceuticals of Collegeville, Pa., which are collaborating on the idea of treating Alzheimer's through the immune system.
People with Alzheimer's have amyloid plaque clumps in their brains, and the vaccine was designed to develop blood proteins call antibodies to attack the plaque. Autopsy studies of three people who had received the experimental vaccine show that the plaque clumps had been cleared from areas of the brain, Gilman said.
Originally, study participants, who had mild to moderate Alzheimer's, were to get six injections over 12 months. But because of the brain inflammation, nobody got more than three and most got only two. The new research looked at psychological tests done 12 months after the first injection.
The study compared test results from patients who had a certain level of antibodies in response to the vaccine versus patients who were given inert injections for comparison purposes.
Not all patients completed each psychological test. Among those who responded to the vaccine, the various tests were completed by 34 to 41 patients; the range for the inert-injection group was 45 to 52.
Results showed no performance difference between the groups in several tests, including two standard ones used for tracking treatment effects. That was no surprise, since the treatment had been interrupted, Gilman said.
But researchers found that the treated group did better than the other group in tests that measure ability to retain memory up to a half-hour. They also found that higher levels of antibody were associated with better scores on the memory tests, further suggesting an effect of the vaccine.
"I think it's a very interesting preliminary finding," commented Bradley Axelrod, a neuropsychologist at the Veterans Affairs Medical Center in Detroit, who didn't participate in the study.
It will take more research to see whether similar therapies can also create detectable differences in mental functioning, and to see precisely what aspects of mental ability they improve, he said.
Elan and Wyeth have started early human studies of infusing antibodies into Alzheimer's patients rather than spurring the immune system to create antibodies.
Dr. Sam Gandy, an Alzheimer's Association spokesman and researcher at Thomas Jefferson University, said human studies of therapies that attack the amyloid clumps are the only way to end the long-standing debate over whether that plaque really causes symptoms of the disease.
Even if they do, scientists will have to figure out how early such treatment is needed to slow the effects of the devastating disease. Gandy said an amyloid-attack treatment might prove effective in preventing the disease rather than stopping it.