The advent of gene technology has provided new and powerful methods for the safe, efficient production of pharmaceuticals, with the bacterium Escherichia coli, mammalian cells, and various yeasts as preferred platforms for the production of such recombinant compounds.1 Early examples include human growth hormone2 and insulin3 produced in recombinant strains of E. coli. Among the most important available recombinant pharmaceuticals are yeast-derived vaccines against papillomavirus4 and hepatitis B infections. Hepatitis B vaccines are based on particles containing the hepatitis B surface antigen (HBsAg) inserted into host-derived membranes.5–7 The success of current vaccination programs against hepatitis B is a result of the development of effective, yeast-derived recombinant hepatitis B surface proteins. Initially, the production of such vaccines was restricted to baker's yeast, S. cerevisiae, but with improvements in biotechnological methods, alternative yeast expression systems have been identified and developed. In particular, the methylotrophic yeast H. polymorpha 8–14 has been found to exhibit many superior expression characteristics, and is currently being used in the production of several vaccines against different subtypes of the hepatitis B virus.7,15In this article, we briefly describe the hepatitis B virus, its subtypes, and the disease it causes. Subsequently, recombinant protein production is discussed, focusing in particular on the application of the H. polymorpha expression system. We describe how a heterologous H. polymorpha strain expressing HBsAg is constructed and how efficient vaccine production is developed based on such recombinant strains.
Finally, we will provide an outlook for alternative vaccine strategies and the development of alternative vaccine candidates.
Virus and Disease Characteristics
Hepatitis B virus (HBV) was identified as the causative agent of serum hepatitis in the 1970s16 after B. Blumberg discovered the Australia antigen.17 Blumberg first recognized this antigen as a serum protein specific for aborigines in Australia. It was only later that the infectious nature of the Australia antigen was identified; it turned out to be the surface protein of HBV that is secreted into the bloodstream of infected patients in large excess over viral particles.18 HBV was found to be endemic in many parts of the world, with more than 2 billion people having had contact with the virus and more than 350 million chronic carriers of the virus.19