Physical, chemical and immunological stability of CHO-derived hepatitis B surface antigen (HBsAg) particles

Recombinant hepatitis B surface antigen (HBsAg) particles derived from Chinese hamster ovary (CHO) cells were stored at various conditions for 12-18 months in their naked form or adsorbed to alum (HBV vaccine). The physical, chemical and immunological parameters during storage at -20 degrees C, 4 degrees C, room temperature and 37 degrees C were investigated. HBsAg particles fully retained the original peptide composition when stored for 6 months, as a dispersion, at -20 degrees C and 4 degrees C; and as lyophilized powder, at all four temperatures. Ten percent sucrose preserved the size, shape and protein content of the naked particles stored at 4 degrees C and -20 degrees C for 18 months as a dispersion or lyophilized. Lyophilization in the presence of glucose, sucrose and trehalose, but not mannitol, further improved the 4 degrees C stability of size, shape and the protein content during 2 years of storage. Stability of the particle's lipid components was inferior to that of the protein components. Dispersions of naked HBsAg and of particles lyophilized in the presence of sucrose and stored at -20 degrees C were the only forms in which the lipid content and composition, including the lipid polyunsaturated acyl chains, were preserved for at least 18 months storage. The level of phospholipid and free cholesterol were most stable in the HBV vaccine which was stored at 4 degrees C; they did not change after 1 year of storage. Preservation of immunogenicity was evaluated according to dose-dependent changes in S-specific antibody titers in sera obtained from immunized BALB/c mice. The ED50 for achieving seroconversion was 0.07 microg/ml/mouse, indicating that the vaccine is very immunogenic. Freezing or freeze-drying of the HBV vaccine results in the total loss of vaccine immunogenicity (in spite of the good chemical stability), while full immunological potency was retained for at least 2.5 years at 4 degrees C. Storing formulated vaccine at 25 and 37 degrees C for 4 and 2 weeks, respectively, did not alter the vaccine potency. This study suggests that the vaccine's physical, chemical and immunological characteristics are sufficiently stable at high temperatures to reduce the need for 'cold chain' transportation.