This post, by Andrew Byrne at the University of Albany, is the first of an occasional series written by undergraduate neuroscience students. If you are an undergraduate interested in writing about neuroscience for the Dana blog, or a professor who might have interested students, please contact Andrew Kahn at akahn@dana.org for more information.
Imagine if Alzheimer’s disease joined the ranks of Polio and the Measles. To prevent it, all you would have to do is stop by the doctor’s office and get a shot every year or so. As farfetched as it may seem, the idea for an Alzheimer’s immunization has been around for the better half of a decade and while we are far from a magic bullet, researchers have uncovered several promising leads.
The idea for an immunization is largely based around the amyloid cascade hypothesis, attributing the neuropathology of Alzheimer’s to aggregates or plaques of the protein beta-amyloid. Originally the toxicity of beta-amyloid was thought to reside in its tendency to form plaques in areas of the cortex like the hippocampus and the amygdala, big players in memory formation and retrieval. More recent studies show that other types of beta-amyloid may be a cause of the toxicity as well.
Researchers determined that targeting plaques with antibodies directed against beta-amyloid might increase clearance from the nervous system while preventing amyloid aggregation, thereby improving cognition in Alzheimer’s patients.
Results thus far have been mixed. Elan and Wyeth Pharmaceuticals recently published a long-term follow up of patients immunized with synthetic beta-amyloid 1-42, AN1792, in conjunction with QS-21, an immunologic adjuvant. The original study was discontinued in Phase IIa clinical trials when some subjects developed encephalitis, or inflammation of the brain. The follow-up, conducted five years after the initial immunization, found that some subjects (referred to in the paper as “antibody responders”) continued to produce antibodies directed against AN1792. In addition, these subjects out-performed placebo groups in several measures of cognitive functioning.
Admittedly the study is not without its flaws. Of the 300 patients originally treated with the vaccine, only 20 percent were deemed antibody responders. The remaining participants either did not produce antibodies or did not produce enough to be of therapeutic value. While one-in-five may not seem like a pharmaceutical triumph, I see it as a big step in the right direction.
So how close are we to an Alzheimer’s vaccine? With at least ten amyloid-targeted vaccines in clinical trials and countless more preclinical animal studies, I’d say a lot closer than we were 10 years ago. New ways of immunizing are being explored, targeting the genome as well as other proteins. For now we will have to wait.
--Andrew Byrne, University of Albany, May 2011