June 14, 2006
A vaccine that would prevent or stop the relentless mental decline of Alzheimer's disease came one step closer to reality with reports that an experimental treatment reduced the buildup of brain-damaging beta-amyloid deposits in mice. Years of additional testing are required, however, to determine whether the vaccine is truly safe and effective in people.
The new vaccine is important, doctors say, because it does not activate a certain type of immune system cell, called a T cell, that is vital for the body's immune defenses. In humans, this kind of T cell is believed to be responsible for the serious side effects that occurred with earlier vaccines. Other scientists are presently modifying these earlier vaccines in an effort to prevent the destructive T cell responses that occurred earlier in some patients. Such modified vaccines might also show promise in the fight against Alzheimer's disease.
The new vaccine, called a DNA vaccine, caused the immune system (in mice) to produce antibodies that neutralized beta-amyloid, the sticky substance that builds up in the brains of Alzheimer's sufferers. Researchers at the Tokyo Metropolitan Institute in Japan tested the experimental vaccine in mice that were specially bred to develop an animal version of Alzheimer's disease. These mice develop deposits of beta-amyloid in their brains as they age and lose the ability to function, similar to people who develop Alzheimer's disease.
Some mice started receiving injections of the vaccine into their muscles at three to four months of age, before any brain plaques had formed. Those mice that were vaccinated had 15 percent fewer plaques at seven months of age, and 38 percent fewer plaques after 18 months. There were no major side effects. The results show promise for helping to prevent the kind of damage to the brain caused by Alzheimer's disease.
Other mice received the vaccine starting at a year of age, six months after brain-damaged plaques had begun to form. At 18 months of age, the mice that had been vaccinated had 40 to 50 percent fewer plaques than unvaccinated mice.
It needs to be stressed that what works as a vaccine in mice doesn't always work in humans, especially elderly humans, who are known to have much weaker immune systems compared to younger individuals. Nevertheless, it is the opinion of alzinfo.org that the DNA vaccine may be a worthwhile possibility for testing in the fight against Alzheimer's disease.
Vaccines: A Troubled History
The search for an effective Alzheimer's vaccine has a troubled history. Various vaccines have shown promise over the years, but so far, benefits have been limited. Some vaccines that appeared promising initially could not be tested further because they produced severe reactions, such as inflammation of the brain in some people.
Researchers are hopeful that the current vaccine, which works by a different mechanism than many of the earlier vaccines, will not cause inflammation or other severe side effects, but this remains to be determined. It is also unknown whether this new type of vaccine will be effective in Alzheimer's patients. The findings were published in the online version of the Proceedings of the National Academy of Science, a journal for medical researchers.
Various vaccines and many new drugs are under development for Alzheimer's disease. The Fisher Center for Alzheimer's Research Foundation continues to fund essential basic research into the underlying cases of Alzheimer's disease, research that may one day prove key to finding a cure for the disabling illness. For more on vaccines and medicines currently under development for Alzheimer's disease, visit the www.ALZinfo.org or the discussion: Frequently Asked Questions about Clinical Trials.
Yoshio Okura, Akira Miyakoshi, Kuniko Kohyama, Il-Kwon Park, Matthias Staufenbiel, and Yoh Matsumoto. "Nonviral A DNA vaccine therapy against Alzheimer's disease: Long-term effects and safety." Proceedings of the National Academy of Science online edition, June 12, 2006, 10.1073/pnas.0600966103.