Hepatitis B surface antigen (HBsAg) derived from yeast cells (Hansenula polymorpha) used to establish an influence of antigenic subtype (adw2, adr, ayw3) in measuring the immune response after vaccination.

As a product of western world biotechnology the yeast (Saccharomyces cerevisiae) hepatitis B vaccine was introduced as antigenic subtype adw2. However, an HBsAg/adw2-vaccine may provide a good but not "optimal" immunologic response for infection with heterologous virus strains. The availability of the yeast Hansenula polymorpha HBsAg in three different antigenic forms (adw2, ayw3 and adr) enabled us to investigate the influence of variant amino acids in the binding of immune anti-HBs after vaccination. Hansenula-derived HBsAg was standardised on the basis of protein content at >95% purity. Standardisation was controlled by monoclonal anti-HBs binding in a well-conserved region. Sera were obtained after immunisation with type adw, ayw and adr vaccines. Direct binding of immune antibodies to homologous antigen (in EIA) was higher than to heterologous antigen except for the adr-related antibodies. Since the binding of the WHO reference anti-HBs was strongly reduced for the ayw and adr compared to the adw antigen, a similar binding profile for the three antigens on protein basis could result in 2-3-fold different anti-HBs level expressed in IU/l. Inhibition of Hansenula-derived HBsAg binding to solid phase monoclonal anti-HBs in enzyme immunoassays after incubation with serum anti-HBs confirmed the differential binding of serum anti-HBs with variant Hansenula-derived HBsAg. This variant (antigenic subtype) dependent reactivity of anti-HBs in immunoassays in combination with a variant specific WHO standard may limit the application of the threshold levels of 10 and 100 IU/l for seroconversion and seroprotection.