Researchers hope to one day treat Alzheimer's with vaccines that prevent or clear the buildup in the brain of a protein known as beta-amyloid. But an early clinical trial of one such vaccine, sponsored by Elan of Dublin, ­Ireland, was stopped in 2002 after some patients developed encephalitis, an inflammation of the brain. Later, autopsies showed that despite the inflammation, the vaccine did clear the toxic protein from the patients' brains.

The Elan vaccine used the beta-­amyloid protein itself to induce an immune response. Now, the National Institute on Aging is sponsoring a new trial of an antibody-based therapy already used to treat immune disorders: intravenous injection of immunoglobulins. The therapy uses a mix of different antibodies, including some against amyloid. Because immunoglobulins have already been used to treat thousands of people with immune disease, scientists say they are unlikely to cause inflammatory problems.