Although their research, just published online in Springer's journal Biotechnology Letters, is still in the early stages, it is a promising first step towards finding an edible vaccine against the neurodegenerative disease.

Alzheimer's disease is the most common cause of dementia and it progresses over a long period of time. It is thought to be caused by the accumulation of human beta-amyloid, a toxic insoluble fibrous protein in the brain, which leads to the death of neurons. Reducing the accumulation of beta-amyloid may inhibit the degeneration of the nervous system and therefore prevent or delay the onset of Alzheimer's disease. One approach is to stimulate the immune system to reduce beta-amyloid in the brain.

Kim and colleagues' aim was to develop a plant-derived vaccine against Alzheimer's disease, since beta-amyloid is toxic to animal cells. Tomatoes are an attractive candidate as a vaccine carrier because they can be eaten without heat treatment, which reduces the risk of destroying the immune stimulation potential of the foreign protein. The researchers inserted the beta-amyloid gene into the tomato genome and measured the immune responses to the tomato-derived toxic protein in a group of 15-month-old mice.

They immunized the mice orally with the transgenic tomato plants once a week for three weeks, and also gave the mice a booster seven weeks after the first tomato feed. Blood analyses showed a strong immune response after the booster, with the production of antibodies to the human foreign protein.

The authors conclude: "Although we did not reveal a reduction of existing plaques in the brain of mice challenged with tomato-derived beta-amyloid this study represents a unique approach in which transgenic plants expressing beta-amyloid protein are used to produce a vaccine." The team is currently looking at strategies to increase the potency of the tomato-based vaccine, because fresh tomatoes contain only 0.7% protein and levels of foreign protein are even lower.

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