Until the early 1980s, the development of vaccines was mainly focused on the employment of attenuated and inactivated pathogens, or on preparations of their disease-causing components. Although live vaccines are highly immunogenic, there is still a risk that a virus may revert to its original pathogenicity. Furthermore, during the production of inactivated live vaccines, the disease-causing agent might retain part of its biological activity so that intact pathogens remain functionally active. The application of both kinds of vaccines can lead to adverse side-effects. Therefore, recombinant subunit vaccines – in particular those that are based on virus-like particles (VLPs) – have gained importance as an attractive approach to modern vaccine development.

The expression system enables a likewise rapid and effective in vivo production of hybrid VLPs that carry antigenic determinants of a particular pathogen within their viral capsid. The recombinant VLPs are replication incompetent, non-infectious and produced in a host (S. cerevisiae) that possesses GRAS status. After cell disruption, hybrid VLPs can be easily obtained in high yield and purity in a single step. Besides their use in vaccine development, recombinant yeast VLPs represent also a unique and alternative tool in heterologous protein production.

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ADVANTAGES
The use of genetically engineered proteins is especially convenient in the production of biopharmaceuticals as they can be produced in sufficient amount and are usually devoid of toxic compounds. Since hybrid yeast VLPs turned out to be antigenic in an ex vivo assay and immunogenic in an animal model, recombinant yeast VLPs bear the potential for being used as particulate subunit vaccine. In addition, yeast VLPs can also be used for the production and purification of foreign (even toxic) proteins.
Further potential application fields of recombinant VLPs are:
- Manufacturing of vaccine
- Presentation of surface-exposed epitopes
- Expression and purification of heterologous proteins
- Non-selective expression of heterologous proteins in vivo
- Analysis of protein/protein interaction in vivo
- Posssible use as a transfection agent.