Dreams of a vaccine to protect against Alzheimer’s have not completely vanished with the discontinuation of AN-1792, a vaccine under investigation by Elan Pharmaceutical.
Early on, studies showed that the vaccine prevented the formation of plaques in the brains of young mice genetically engineered to produce amyloid and reduced the formation of plaque in older mice. In humans, the vaccine showed that some patients developed amyloid antibodies. The studies then went into a phase IIA trial that involved about 360 subjects with mild to moderate Alzheimer’s.
Unfortunately, the vaccine trials were discontinued after four participants developed inflammation of the brain and spinal cord. Less then two months later, eleven subjects developed the same symptoms, and the trial came to an end.
Many scientists say the quest for an eventual vaccine is far from over. Some researchers are exploring ways to refine the AN-1792 vaccine, possibly by targeting a portion of beta amyloid rather than an entire fragment, which experts theorize might have caused the inflammation. Other researchers are looking for ways to interfere with the development of beta amyloid by stimulating the patient’s immune system to identify and eliminate the destructive plaques, which is known as active immunization. Still others are exploring passive immunization—the administering of routine injections—as a way to prevent Alzheimer’s.
Recently, scientists at the Johnnie B. Byrd Alzheimer’s Center and Research Institute in Tampa, Florida, reported some promising results with a vaccine tested in transgenic mice. The mice were given routine beta amyloid immunization throughout most of their adult lives and then tested at two intervals: as adults and in old age. Results showed that the immunotherapy delivered partial, or even complete protection, against cognitive decline at both test points. The tests measured several different cognitive abilities including memory, working memory and recognition.