A range of different approaches are being taken to develop Alzheimer's vaccines, aiming to incite the immune system to step in and block various known biochemical mechanisms of the disease. From ScienceDaily: "Tang and his colleagues at OMRF previously had identified the cutting enzyme (known as memapsin 2) that creates the protein fragments believed to be the culprit behind Alzheimer's. In the current study, researchers used mice that had been genetically engineered to develop symptoms of Alzheimer's, then immunized the animals with memapsin 2. ... What we saw is that the mice immunized with memapsin 2 developed 35 percent fewer plaques than their non-vaccinated counterparts. Those immunized mice also performed better than control mice in tests designed to assess their cognitive function. ... Tang's work with memapsin 2 also has led to the creation of an experimental drug to treat Alzheimer's disease. That drug, which works by inhibiting the cutting enzyme, began human clinical trials in the summer of 2007."