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February 28,  2001

Plant Research International and RIKILT have made a significant breakthrough in the development of plants which produce proteins that can be used for the passive vaccination of people and animals. The antibodies found in these plants are much more similar to human and animal antibodies than was previously thought possible and will therefore be more effective. The results of the two institutes work has been published in PNAS of February 28, 2001.

Antibodies are proteins with a characteristic and special structure, a part of which is involved in the recognition of pathogens. Another part is concerned with the immune reaction that follows this recognition. The complex of different sugar molecules (glycan) bound to the protein is also involved in this process.

Plants that make antibodies

Previously Plant Research International already succeeded in developing plants which produce antibodies that can recognise pathogens. However, the biochemical reaction whereby sugar complexes are bound to proteins - glycosylation - is different to that which takes place in animals. As a result, the antibodies made in plants are less effective. Part of the sugar complex is so different compared to animal antibodies that an undesirable immune reaction can occur against the antibodies. 

The researchers at Plant Research International therefore equipped tobacco plants with a gene that codes for an enzyme responsible for an important step in the typical glycosylation event in animals. This enzyme transfers galactose molecules to the sugar complex. Previous studies had shown that these galactose molecules are important to a proper immune reaction and yet do not normally appear in the sugar complex of plants. 

The right sugars

A joint analysis by RIKILT and the University of Rouen has proven that the researchers have been very successful. Thanks to the extra enzyme, galactose molecules were connected in the correct position to the sugar complex in tobacco plants. Evidently, the animal enzyme works in the right place at the right time in tobacco plants.

Part of all proteins in the tobacco plants had a glycosylation pattern more closely resembling that of animals. The plants didn't appear to be affected in any way, indicating that the functionality of the proteins in the plants was not drastically altered.

By crossing the tobacco plants with plants that produce antibodies, the researchers now had plants which produced antibodies that were glycosylated in a more animal-like manner. Consequently, the antibodies were more similar to those found in animals and could do their work more effectively as a result. 

Application

The success of Plant Research International and RIKILT represents a vital breakthrough in the development of plants that can be used for passive vaccination. Passive vaccination involves people or animals being injected with antibodies that can react to specific pathogens, for example
those of tropical diseases. This means temporary protection can be given against the disease without having to vaccinate with debilitating pathogens. 

Benefits

Currently, the antibodies used for passive vaccination are produced in animal systems, which is often an expensive process. Using plants instead would lead to serious savings in costs and also prevent potential problems with animal pathogens in the antibody preparation. In addition, the
plants containing antibodies can also be administered as special 'medicinal food', whereby livestock can be protected against disease via their feed rather than by using injections. 

Company news release
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