Preparation and Immunogenicity of a Picha pastoris-derived Hepatitis B Vaccine Containing PreS1, PreS2, and S Epitopes

The preparation and immunogenicity of a novel hepatitis B vaccine containing preS1, preS2, and S epitopes were investigated in this study. A Pichia pastoris strain GS115-SS1S2 harbouring two chimeric HBsAg gene constructs, SS1 and SS2, was cultivated by high-density fermentation. 300-600 mg/L of the expression level was achieved through 48-72 h methanol induction. SS1S2 antigen was extracted and purified by silica adsorption, HIC and SEC to 99% purity from the harvested cells. 82 mg purified antigen could be achieved from one liter of fermentation culture. The immunogenicity of the purified antigen was evaluated in NIH mice. Three groups of female NIH mice, 14-16 g in weight, were injected once intraperitoneally with 2.5, 0.625, 0.156 μg of each of the two vaccines: SS1S2 or a commercially available S vaccine. Part of the mice were bled in 30 days after injection to compare the ED50 of the two vaccines. For the SS1S2 vaccine, the ED50 is 0.46, 0.29, and 0.84 μg, respectively for the preS1, preS2, and S antigens. For the S vaccine, the ED50 is 0.99 ug for the S antigen. Another part of the mice were bled in 7 or 14 days to detect preS1, preS2, and S antibodies. Higher ratios of mice were seroconverted for preS1 and preS2 antibodies as compared to the S antibody in these two time points. These results suggest that the SS1S2 vaccine may be more immunogenic than the conventional S vaccines.