WASHINGTON, Nov. 25 (Xinhua) -- U.S. researchers have developed a DNA vaccine that successfully held off Alzheimer's disease in animal tests. The vaccine, if proven safe and effective in human trials, could reduce dementia cases by half.

Tests in mice have shown that the DNA vaccine reduced accumulation of both types of toxic proteins associated with Alzheimer's disease, namely tau and beta-amyloid, without triggering severe brain swelling that earlier antibody treatments caused in some patients, researchers at the University of Texas (UT) Southwestern Medical Center said Tuesday in a press release.

The study, published in the medical journal Alzheimer's Research and Therapy, showed that the vaccine prompted a 40 percent reduction in beta-amyloid and up to a 50 percent reduction in tau, with no adverse immune response.

"This study is the culmination of a decade of research that has repeatedly demonstrated that this vaccine can effectively and safely target in animal models what we think may cause Alzheimer's disease," said Dr. Roger Rosenberg, lead author of the study.

"I believe we're getting close to testing this therapy in people," said Rosenberg, who is also founding director of the Alzheimer's Disease Center at UT Southwestern.

The researchers believe that if amyloids and tau are indeed the cause of Alzheimer's disease, achieving these reductions in humans could have major therapeutic value.

"If the onset of the disease could be delayed by even five years, that would be enormous for the patients and their families," said Dr. Doris Lambracht-Washington, the study's senior author.

"The number of dementia cases could drop by half," she added.

Alzheimer's disease is a degenerative brain disease characterized by symptoms such as difficulties with memory, language, problem-solving and other cognitive skills. These difficulties occur because neurons in parts of the brain have been damaged and destroyed.

According to the non-profit Alzheimer's Association, 5.7 million Americans are living with Alzheimer's disease, and the number is projected to rise to nearly 14 million by 2050. It is the 6th leading cause of death in the United States.