Hepatitis B vaccine produced in yeast

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Abstract
A gene encoding the 226 amino acid hepatitis B surface antigen (HBsAg), subtype adw, was cloned into a generalized vector for the expression of heterologous genes in Saccharomyces cerevisiae. The 5′ end of the genomic HBsAg gene was replaced with a chemically synthesized DNA segment that conserved the amino acid sequence of the protein but utilized DNA sequences that optimize translation initiation in yeast. High-cell-density fermentations of laboratory strains of Saccharomyces cerevisiae have been developed in which HBsAg production increases linearly with respect to cell mass. The HBsAg is present as a lipoprotein particle in cell lysates and has been purified to homogeneity. The evidence presented indicates that the HBsAg particles may be formed during lysis of the yeast cells. The purified HBsAg particles have a morphology similar to that of the 22 nm particles present in the serum of human chronic carriers of hepatitis B. The reactivity of the yeast-derived HBsAg particles with a series of monoclonal antibodies is essentially identical to that of human plasma HBsAg. By this analysis, therefore, the structure of the HBsAg protein is similar in yeast and in human particles. The purified yeast HBsAg particles were formulated with alum adjuvant and subsequently were shown to confer immunity in chimpanzees to challenge with two heterologous serotypes (adr, ayw) of hepatitis B virus.