CORDIS - EU research results

Vaccine against oncogenic Human Papillomavirus produced in soybean protein-bodies

Final Activity Report Summary - HPV-SOYBEAN (Vaccine against oncogenic Human Papillomavirus produced in soybean protein-bodies)

The rapid growth in molecular biology and medicine in recent years have identified many new proteins with promising potential in treatment or prevention of diseases. One of the major obstacles in their widespread use is lack of production capacity, even though plants offer economical and inherently safe alternatives to present systems which are based on microbial fermentation or mammalian cell culture. Another obstacle to the use of many recombinant proteins in global vaccination programmes are the costs connected with their purification, storage, cold chain preservation and administration. In the current project, we showed that soybean seed was well suited for high level accumulation of subunit vaccine protein because of its long time storage at ambient temperatures and straightforward oral application without the need of extensive purification.

The current trend in the development of plant-based pharmaceuticals is towards the utilisation of seed based, rather than plant leaf based production. Expression in seed often results in increased levels of foreign protein accumulation and greater planta stability. It also provides a final product in the form of dried seed that can be stored for long term without loss of biological activity and can be easily processed, formulated and transported. Mature soybean seeds (glycine max) typically have extremely high protein content, ranging from 35 to 50 %, which could be extracted in cold water (soymilk) and further processed using available technologies. An additional advantage of using soybean is its elevated levels of soybean trypsin inhibitor, alpha-amylase and other defense proteins. These plant products may potentially enhance the stability of the seed-based vaccine after oral administration.

The aim of this project was to provide proof of concept for the production and accumulation of pharmaceutically important proteins in soybean seed. The major scientific question was whether the system allowed for expression of pharmaceutical proteins in both sufficient quality and quantity.

During the course of work we established that:
1. expressed proteins were correctly folded with properly formed disulphide bonds;
2. most, if not all, expressed protein was present in correct multimeric complexes;
3. the expressed protein was enclosed in Endoplasmic reticulum (ER) membrane derived vesicles, i.e. protein bodies which were stable during the maturation, desiccation and subsequent storage of the seed;
4. the protein accumulated to high levels of about 2.5 % of total seed protein, which translated to approximately 1 % of the seed weight. This was, to our knowledge, the highest per kilogram yield of plant-made pharmaceutical protein reported in the scientific literature. Such high expression levels allowed for economically feasible vaccine production under high biosafety level containment conditions, such as in a production greenhouse and, for some applications, also allowed for direct oral application without the need of prior purification or concentration;
5. raw non-purified seed extracts administered orally to mice induced both systemic IgG and IgA, as well as mucosal IgA antibody responses and were particularly efficacious when used in a parenteral prime-oral gavage boost immunisation strategy.

It was anticipated that these results would guide the development of a valuable soy-based oral immunisation strategy with its low cost per unit vaccine production capability and suitability for processing into oral delivery materials that would be broadly useful for disease prevention both in animals and humans.